I'm a newbie baker and always wanted to try to decorate cookies with hard frosting. I finally found the best recipes for royal icing. Meringue powder was the key ingredient. Wilton makes it and you can get it at and cake supply store or crafts store like Michaels. It's really easy and comes out fantastic!
I also bought Wilton's gel food coloring that makes coloring the royal icing easy and the colors are really bright.
Also, I used the cake decorating bags and tips. It makes clean up quick and they are easy to use.
If you want to do lines, make the icing think enough so the line doesn't spread out. If you want to fill an area (called floating) you want thinner icing. One way is to outline your cookie with thicker icing and then fill it with thinner icing that will spread.
Anyway, the best way to learn is to experiment and play with the icing. Have fun! I learned how to do it last easter, too and had a blast! I used an easter egg shaped cookie and had so much fun making my cookie "easter eggs"!
Also, the thinner the icing, the longer it will take t o dry. It actually took a few days for them to dry the first time I made them, but less than a day the second time. Maybe the weather had something to do with it...
And for eyes, I had fun using some of the pre-made sprinkles and using icing to "glue" them down.