Thank you for all the tips. I do make sure I line up selvages, not cut ends and make sure my fabric lays flat on the fold. I then iron iron iron until it is nice and crisp and flat. I line the fold at the bottom edge with the selvage away from me then square it up. I'll have to try the two ruler trick. I also don't touch the fabric that I am cutting when I am cutting multiple strips.
I just got an Eleanor Burns Log Cabin book and she recommends tearing off a strip of fabric to make sure that you are perfectly straight on the grain. I'm hesitant to tear as I also don't want to stretch anything but maybe I'll try it with some scrap fabric and see if it helps. I saw a recent huge discussion about tearing vs cutting on this board.