After reading what the rest of us do for pressing, I think it really comes from practice. You will learn where a seam needs to be open, or pressed to the dark, by doing.
So don't be shy. Step up and do the piecing. And if you find your seam is too bulky after you have pressed it one way, who's to say you can't go back to the ironing board, and re-press it a different way before you sew to the next piece. :lol: That's me - :roll: - re-doing something. It really does not take long, and you learn best by doing!!