Other than 1/4 inch seams, when you finish a block, square it up to a certain size- 10 inch or 12 inch or whatever. When you finish your blocks, trim them so they are all the same size and your quilt blocks will fit better. If it is a sampler quilt, you may have to cut some of the block off or even maybe add a small border to make each block the same size.
Hope this helps.