Try do well on the AFOQT and the TBAS, you will put a max of 201hrs towards your PCSM score (after that the hours/ratings/licenses don't really matter all that much). I don't think that GPA is a factor with OTS slots anymore (very recently) other than over the minimums. The AFOQT is not a hard test but certainly worth getting the study guides for. The TBAS is a different animal... some say play video games/flight sims... personally I don't play much of those and I didn't do so hot on that test. The first parts were easy, the last parts were very hard - either way you don't get a score from the TBAS specifically. That test is kinda hush-hush, but read what you can about it.... and when you get in there... read the directions very, very carefully - soak them in deeply.
My AFOQT pilot was 96, with max flight hours and the TBAS it dropped my PCSM to 95 - not the best, but oh well.
Good luck!