I think Wilton has a tutorial on their site. I haven't been there in years, but I could swear they have one.
go to wilton.com
Browse decorating techniques. I don;t have time to surf. But this will get you started:
Here is another link for you to browse through. It has several techniques.
I saw these links online & saved them for inspiration and technique; hope it helps...
here's another...she used tip 3 and 5.