Cassandra,
It depends on how big you want your quilt to be. How big you want your squares to be and you have to decide if you want to use batting or flannel for the middle. There are many posts on here about rag quilts, if you do a search I'm sure you will find a lot of information. I made my squares 6 1/2" and used flannel for the batting and my seam was 1/2". They go together very quickly. If you need to know anything else, just ask. Even if you don't know yet how big you want to make your quilt, you can always start it and then always add more blocks. There is no way to mess up a rag quilt. Good Luck! :D Please be sure and post pictures.
By the way your avatar is very pretty, did you take the picture?