Usually I press seams to one side. Sometimes, if there's a lot of seams meeting in one place, I'll press the seams open.
Pressing is a tricky thing. You have to be careful to not stretch the bias of the fabric, but you have to at least pull the fabric taut, so you don't get puckers. Try pressing from the right side of the blocks, instead of the seam side. You might also try "finger-pressing" your blocks first, before taking them to the ironing board, then press with the iron. Inspect your blocks after pressing but before assembling them into rows - if there's a pucker, you can always fix that with a little shot of steam.