Use a sharp knife: Using a sharp kitchen knife will ensure your cookies have clean edges.
Carefully pipe frosting: I highly recommend using a piping bag for the frosting rather than a knife. You will get a clean line of frosting that will look neat. For tips on making a piping bag from a zipper bag, check this out.
Prop them up: If you are making the cookies a day ahead of time. you may want to place half of toothpick on the back side of the cookie to hold it up overnight.
Dietary: Use low calorie, gluten free or dairy free versions as you need them.