the biggest thing is that you don't want to hit the repeat evenly, you want to see mainly one color in some of the blocks, there really isn't a magic formula, it depends on how much of the print that you want to see in each block. it really depends on what you want to see in each of the pieces. obviously there is advantages to cutting bigger blocks like less sewing, the smaller ones can make it easier to have similar or close to the same blocks.