the idea of 'press to the dark' usually works because there is less chance of seeing the seam thru the front. And, it is usually a good rule to follow (consistency is good). But, there are always exceptions. There are times when you will do 2 sections opposite so the seams will nest nicely. If I have one long 'clean' piece and the attaching piece already has seams, I will usually press to the flat open piece (less bulk). One thing I always do with a new block is to make ONE BLOCK. This way I can figure out what works best for the whole construction. It may feel like it takes a bit more time, but in the long run, it saves a lot of time! I rarely, rarely, rarely ever press open because I think it allows for more chance for batting to show and stitch in the ditch has nothing to grab onto.