There are a number of products on the market that will simplify the process of making berries. Plastic die-cut circles are great. I prefer a heat resistant Mylar circle. It is possible to make the circles with regular plastic circle die cuts, however. We will discuss this alternate method. Check our links page for a source for the Mylar circles.
I also like a circle template that I picked up at an office supply store. It isn't necessary but it is nice.