Thanks so much for all the great advice. Most definitely I'll need to practice the braking technique.

The article that was written by Sheldon Brown is located here:
http://www.sheldonbrown.com/brakturn.html

This does confirm what most of you are telling me about braking. And your advice on using the arm signals is very helpful. (I'll want to get more comfortable riding before I even attempt to ride with a group!)