Simple Decorations are made by making patterns in the frosting, before it has set, with a small metal spatula. These decorations can be done on both the sides and the top but and the frosting beneath does not have to be perfectly smooth before decorating:

Other decorative touches are applied either before or after the icing has set. Some frostings and especially glazes benefit by sitting in the refrigerator for an hour before serving or decorating. If you place anything perishable on the cake, it must be kept refrigerated. 

For a complete list of decorating styles, click here. Some frostings and especially glazes benefit by sitting in the refrigerator for an hour before serving or decorating, if desired.

Press a cake-decorating comb into the sides and top of a frosted cake, before it has set.  Pull it across the icing, making a U shape from one line to the next to form waves. The tines of a fork can be used to make the same design. Clean either tool often.  

In the same manner, the edge of a serrated knife can be used to make designs in the icing. Hold it on its edge, and lightly sweep it from the farthest point of the cake, bringing it towards you. 

Or, use a small offset spatula to pull the still-moist frosting straight up, creating points. Other designs can be made in the icing with an icing spatula.

Before the icing has set, chopped toasted nuts, colored sugar or coconut, or even shaved chocolate, can be sprinkled on top. For a birthday present cake, cut sheets of rolled fruit leather into 3/4 inch strips. Place strips on frosted cake to resemble a wrapped package. For a bow, loop strips on top of cake. 

You can even make designs with very small candy such as gumdrops or gummy bears on the top for other decorations. 

Decorate with fresh fruits such as whole raspberries, blueberries, blackberries, strawberries, sliced kiwi fruit and orange sections. These are good choices because they do not brown, and can be placed on the cake just before serving.

Nuts placed in the top of the cake look so beautiful. The shape and color of sliced almonds lend themselves well to a frosted cake. To press halved nuts:

1. First, lightly dust the cake with confectioner's sugar. 
2. Halve several intact almonds with a paring knife. 
3. Arrange the halved and additional whole almonds in a fleur-de-lis design around the perimeter of the cake. Or, create almond flowers; place tips of sliced almonds in frosting to form a flower using almonds as the petals. Place a small candy in the center of each flower.
4. Press nuts in the side of the icing (see below).

Sometimes a cake decoration can be made, as simple as pressing toasted nuts or colored sugar and coconut or shaved chocolate into the sides of the frosted cake. You will need about 1 cup to cover the sides of a 9-inch cake. Other goodies are crushed peppermint sticks or peanut brittle, whole peppermint patties, cookies or life saver candies pressed in a pattern, chocolate chips, M & M's, licorice sticks etc. To do:

1. Frost cake, and do not let it set. 
2. Place goodies in a wide mixing bowl, and then pick up platter or cake round in one hand over the bowl.  
3. With the free hand, hold at handful of goodies and lightly press them with the palm of your hand against the cake so the excess falls in the bowl below.  If using chocolate, lightly place it on the sides, and use a spatula to gently press the shavings in. This is done so they won't melt.  
4. Then, let the frosting set before serving.

Baked goods are sometimes just decorated with a light dusting of sifted confectioner's sugar or cocoa powder. Dust lightly or as liberally as desired through a shaker, sieve, strainer or sifter. 

For the sugar, do so right before serving because it will gradually dissolve. There is nondissolving sugar available. 

To dust:

1. Place the baked good on a wire cake rack. 
2. Put several spoonfuls of confectioner's sugar or cocoa powder in a small shaker,  fine mesh sieve, strainer or sifter. 
3. Hold it over the baked good, and lightly tap it with a spoon while moving it.

For a more dramatic look, a design, lace paper doily or simple shapes can be placed on a frosted  cake or cupcakes before dusting to make beautiful designs where the stencil cut-outs are. Perfect ingredients for dusting can be: sifted confectioner's sugar or cocoa powder, flavored or tinted sugar, finely chopped nuts,  or ground cinnamon, mixed with sugar.

There are store bought stencils or you can make your own.

For the sugar, dust the stencil right before serving because it will gradually dissolve. There is nondissolving sugar available. 

1. Freeze the cake for 15 minutes before stenciling so the stencil will not stick to the cake.
2. Center a stencil on top of a cake. 
3. Put several spoonfuls of confectioner's sugar, cocoa powder or cinnamon in a small, fine mesh sieve.  Hold it over the baked good, and lightly tap it with a spoon while moving it. 
4. When done, carefully remove the stencil, doily or toothpicks so as not to spill extra on the cake, and voila ! A beautifully dusted design.

Another great way to dust a cake is to use a stencil and dust with both confectioners' sugar and cocoa powder. Make two stencils, one for where you want to see the cocoa powder and one where you want to see the confectioner's sugar, making sure neither overlap. Place the stencil on top of the cake and dust with confectioner's sugar (the lighter color, first). Carefully remove the stencil. Be very careful not to disturb the cocoa powder, and place the second stencil on top of the cake again, this time making sure that the openings are on the parts of the cake that have not been dusted with confectioner's sugar. Dust with cocoa powder, carefully remove the stencil. When you remove the second one, you'll get a very graphic two-toned design.

VARIOUS WAYS TO TRANSFER A DESIGN: Transfer a cartoon character, design or portrait printed from the internet or any source, onto your cake.

Pin-Outlining
This is the easiest method.  It is only suitable for very simple designs.

1. Trace design onto parchment or waxed paper.
2. Cut out the traced design.
3. Ice cake. Let icing crust.
4. Pin or hold design on cake and trace or prick the outline onto the cake with a pin or toothpick.

Gel Transfer
This is a fast method, but it is difficult to use for very intricate designs.  It produces a mirror image.

1. Tint Piping gel with either gel or paste colors so it is visible against the icing on a cake or it contrasts with a cookie.

2. Put it in a pastry bag fitted with a #1 tip or a plastic squeeze bottle (my favorite). 

3. Draw a pattern on a piece of wax paper using an indelible marker. 

4. Turn the wax paper over so the ink in on the backside. Spray backside with a light coating of vegetable oil spray. 

5. You can lay the wax paper on top of a design and simply trace with Piping gel !  

6. CAREFULLY place side with gel design on top of cake or cookie – it’s best if you have let the frosting harden for a few minutes if decorating a cake. (If decorated with sparkling sugar, place right side up, if you can). 

7. Carefully press the gel with your fingers – gently -- and then lift the wax paper off. The design will have transferred to the cake or cookie. You should be able to get two or three transfers from each sheet of wax paper.  

Pouncing
This method is somewhat tedious, but with it you can reproduce very intricate, tight designs.

1. Trace design onto parchment or waxed paper.
2. With pin or pouncing wheel prick through the design.  The more intricate the design, the closer together the pin pricks must be.
3. Ice cake. Let icing crust.
4. Put parchment or waxed paper in place on cake.
5. With a small brush, push cocoa powder (or confectioners' sugar on a dark cake) through the holes in the paper.
6. Very carefully, remove the parchment or waxed paper.

Royal Icing Pattern Press

1. This method is good for a design that must be repeated a number of times.
2. Using a permanent marker (that is, a Sharpie), trace the design onto an appropriately-sized piece of Plexiglas.
3. Glue a handle onto the Plexiglas on the side on which the design is traced.
4. On the other side of the Plexiglas, pipe the design with royal icing. Overpipe. Let dry, then overpipe again. Dry thoroughly.
5. Let buttercream icing crust before using the press. Use on rolled fondant before it crusts.

Piping Gel Pattern Press
This method is also good for designs that must be repeated a number of times, but it has the added advantage of being flexible, so that it can be used on curved surfaces.  It produces a mirror image.

1. Cover design with parchment paper.
2. Trace over design with lightly-tinted piping gel from a small hole cut in a parchment bag (approximately tip #1.)
3. Let piping gel dry.
4. Let buttercream icing crust before using press.

Rice Paper Outline
With this method you can do very intricate designs.

1. Trace design onto the smooth side of a piece of wafer paper using a food color pen.
2. Cut out the wafer paper very close to the design outline.
3. Coat the rough side of the wafer paper witha think layer of clear piping gel.
4. Lay the wafer paper gel-side down on the iced cake.  
5. Outline and fill in the design with buttercream, marshmallow creme flow-in, or piping gel.

Piping Gel Plaque
Use this method if you want a stained glass effect and you want to do your design ahead of time.  It produces a mirror image.

1. Cover design with parchment, tracing or onionskin paper (no waxed paper.)
2. Outline and fill in completely with piping gel.
3. Let piping gel dry for at least 24 hours.
4. Ice cake. Let icing crust.
5. Turn paper over so piping gel design is on the cake.
6. With damp sponge wet the paper until it easily pulls off the piping gel.

Rice Paper with Piping Gel
With this method you can do very intricate designs with piping gel, food colors or the air brush.  It produces a mirror image.

1. Trace design onto the rough side of a piece of wafer paper using a food color pen.
2. Turn the wafer paper over.  Then either (1) Outline and fill in completely with piping gel, or (2) Coat entire surface with a think layer of clear piping gel; then, using a water color brush dipped into paste or liquid food color, tint the areas to be colored, or (3) Lightly airbrush colors into proper places; dry, then coat with a thin layer of clear piping gel.
3. Set aside to dry.
4. When you are ready to use the wafer paper design, turn it over and brush the underside with clear piping gel, then lay it on the iced cake.  Outline the edges with a border of buttercream icing.  This should be done one day in advance of serving the cake.

Color-Flo (Run Sugar)
This method produces a keepsake piece which can be very detailed.

1. Cover design with waxed paper.  Outline with royal icing and a tip #3.
2. Thin down the royal until it resembles free-flowing syrup.  Add colors as desired.
3. From a small hole cut in a parchment bag, flow the thinned icing into the outlines.
4. Allow 24 to 48 hours for the piece to dry.  Ease it gently off the waxed paper.
5. Do not place the plaque directly on a buttercream-iced cake. Elevate it with sugar cubes, so the buttercream icing will not break it down.

Frozen Buttercream
This method is easy and fast. It produces a mirror image.

1. When you find the pattern, have it copied in reverse of how you want it to look. When you get the size and design you want, tape it to a hard surface (I use a flat cookie sheet). Then tape a piece of parchment paper over it. You can also cover a design with window glass and then tape a piece of waxed paper to the glass. 
2. Then do an outline of your design in black or any colored buttercream icing - stick it in the freezer. When the outline is hard and optionally fill in your design. If filling in, to strengthen your design, cover the entire thing with about 1/4-inch layer of buttercream that you will use to ice the cake with. Yes, the whole layer - you are actually working on the bottom! Don't spread a layer of buttercream if you aren't filling in. 
3. Freeze the design (still on the cookie sheet or window glass) until hard.
4. When your cake is ready, remove the design from the freezer. Then flip the picture over and lay it buttercream-side down on the cake. Carefully peel the parchment paper back exposing the picture.  
5. When it thaws it will appear as though the picture was done "freehand" on top of the cake.

P.S. You can always transfer a design/picture to the cake using a projector.

WAYS TO FILL IN A DESIGN: You can fill in the outline of the design right away but it is easier to work with if you wait 2 hours or longer. It will also prevent colors from bleeding together if the outline is dry before filling it in. 

Now use a slightly larger decorating tip (or squeeze bottle) with Piping gel or icing. (Use gel or paste colors), pipe the outline, working a small area at a time. Work from the outside towards the center.

If using icing, flood just inside the line. Use a slightly damp #2 or #3 sable brush, squeeze the bristles flat between your fingers. Then use it to brush icing towards the center of the design. The paintbrush should be damp. If it is too dry, the icing will become rough and uneven.  If it is too wet, it will make a puddle. The brush should be held at a 45 degree angle and long strokes should be used starting at the top edge of the petal or leaf and continue to the base to avoid ridges.

You can also use a glaze made from 2 pounds powdered sugar, 1 tablespoon clear vanilla, 1/2 teaspoons almond flavoring, 1/4 teaspoon salt and 3/4 cups water, tinted with gel or paste colors. The amount of water can vary. Mix it to a consistency that works best for you.

The thinner glaze is easier to pipe into the design, but a thicker glaze is needed if you are using it on a cupcake with a surface that's not level. If your glaze is thin you need to be careful filling in the design or it will overflow the outlines. It crusts quickly, so complete one area at a time, working from the outside to the center of each section. 

The glaze can be kept refrigerated for several weeks or frozen for several months. Parchment is more economical if you only use this method occasionally. If the glaze is saved it will separate in the bags. Pinch the open end of the bag and knead the bag to re mix it. A small piece of tape can be placed over the end when storing the bags to prevent the glaze from leaking.

Petal or luster dusts can be mixed with lemon extract and painted onto the glazed areas after they are dry. It takes 2-8 hours for it to dry enough to be painted on. Smaller areas dry quickly. Larger areas take longer. If you attempt to paint on them before they are dry the glaze will dent.

Make sure you use good support under your cake when  using the glaze. If the cake board bends the glaze surface will crack.

some information adapted from shavkin.com