Royal icing is most often a royal pain in my butt but the more and more I work with it, the easier it is. Now there are tons of recipes out there and my advice is to keep searching for one until it fits you. Here is the latest recipe I used.
1lb Powdered sugar
2 Egg whites
1 Teaspoon lemon juice
1/4 cup water
You can also use meringue powder, go here for an easy recipe using meringue powder.