When you're making "stand-up" butter cream decorations, the thickness of your icing is important. I usually use tweaked version of Wilton's buttercream recipe.
Wilton's Buttercream Recipe My Tweaks to Wilton's Buttercream
1 cup solid white vegetable shortening 1/2 cup vegetable shortening
1 teaspoon Wilton Flavor 1/2 cup salted butter
2 Tablespoons milk or water 1 teaspoon Wilton Vanilla
1 pound pure cane confectioners' sugar 2 Tablespoons water
1 Tablespoon Wilton Meringue Powder 4 cups pure cane confectioners' sugar
A pinch of salt (optional) 1 Tablespoon Wilton Meringue Powder
A few notes: When you're going to be coloring your icing, make sure you use the Wilton (colorless) Vanilla (you can buy this from Michael's or AC Moore) so that it doesn't make your oranges and greens "muddy". Also, in the pictures below I doubled the recipe. This recipe makes the "thick" icing version. To thin your icing (make it more spreadable), add water slowly until it reaches the desired consistency. If you thin too much, add more powdered sugar.
Combine and cream wet ingredients (butter, shortening, vanilla and water).
Add powdered sugar 2 cups at a time, mixing well in-between. Add meringue powder and mix til smooth.
Ice the tops of your cupcakes with a thin layer of the white icing. Transfer some of the icing from your mixing bowl into a smaller bowl and add a little water, mixing between every few drops, until the icing becomes an easily spreadable consistency.
Now for the fun part! Pumpkin time...
I found it's helpful to practice designs when you're learning to decorate cakes - instead of messing up a dozen cupcakes with the trial and error approach. Tape two paper towels down on a flat surface. Then tape two pieces of wax paper (on top of each other) on top of the paper towel. Set aside some of your icing as "practice icing" so you can practice the shapes you're making and re-use the same icing until you get it right. (Then toss the practice icing...just in case!)
Transfer more of the icing from your mixing bowl and add a few drops of orange gel coloring (you can buy this at Michael's or AC Moore). The gel coloring is important because regular (liquid) food coloring will change the consistency of the icing. The gel doesn't!
The pumpkin body is made using a size 12 tip. You'll also need a piping bag (you can buy disposable bags at craft stores) and a coupler (here's some information about how to use a coupler).
First make a ball of icing. To apply, point your tip straight down just above the surface. With consistent pressure, start piping icing and raising your tip slowly as the ball forms. Keeping the tip lower to the surface will let the ball increase its diameter.
Next, you're going to make ridges up the sides of your ball. Start piping at the bottom, slowly lessening pressure as you reach the top. The top will be a little messy where all your ridges come together. Don't worry! It's not a big of a deal since there will be leaves/vines covering most of the top.
Next, practice your leaves. Mix some green icing (you wont' need too much). I used the Wilton "Leaf Green" gel.
Use a medium leaf tip to make the leaves. You'll need to hold the tip so the "V" is perpendicular to the surface. Use your practice area to play with the different leaf types. Use more pressure when beginning the leaf and as you move away, lessen the pressure.
Once you feel comfortable with your pumpkin and leaf skills, put them all together on your cupcakes!
I used another tip (a tiny hole - either tip 2 or 3) to make little vines around the top. Cute little curls are never a bad thing, and add a lot to these little pumpkins!
Now go impress your friends!