I have had more fun with my samplers than any of the quilts that just repeat the same blocks. Too many free patterns out there to worry about paying for some.
I got all of my patterns from www.quilterscache.com. The only "rule" that I really would stick to, is that you choose blocks that end up the same size. That is really important. Also, sashing is a really good idea because it separates the blocks a little so you can see them all individually. You are going to want to pick blocks that you can do, but that are challenging too. That's what I like about quilters cache blocks, you can see the level of difficulty. I also think that the instructions are so good there, that they are hard to mess up.