Sugar cookies, by definition, should be pretty simple since they're comprised mainly of butter and sugar. The problem is, they're fairly labor-intensive and royal icing is tricky to master. I'm no expert, but here are some of my tips to ensure that your cookies come out looking good and tasting even better.
1. If you can, make the dough ahead of time (I like this recipe).
2. Cut out shapes with cookie cutters, bake and then let cool.
3. Make icing.
In a bowl of an electric mixer with the whisk attachment, combine:
4 cups sifted powdered sugar
3 TB meringue powder
10 TB of warm water (add more as needed)
Beat for 8 minutes on low speed Most people swear by making one stiff icing to outline the shape of the cookie and then filling it in (also known as "flooding") with a thinner frosting (made by adding a little water). I prefer to make only one frosting that's neither stiff or runny (somewhere just in between) that can most accurately be described as the consistency of toothpaste.
5. Transfer frosting to pastry bags or into squirt bottles (my preference).
6. Outline cookies and then fill the inside using the pastry tip as a way to add and spread the frosting as you go.
7. Add sprinkles/edible pearls/sanding sugar before the frosting sets.