I generally make a plan to identify the steps it takes to put the blocks together (starting from the cutting diagram). If it is a large quilt with lots of repetition, I sometimes finish one step of the process for all blocks, then move on to step 2. If I get bored, I take a sub-set of the pieces and finish a subset of the blocks. However, I NEVER assemble the rows until I have all of the blocks done. I find it easier to "park" a project as blocks or pieces than partly assembled with pieces still to do.