I would say that the best way to get the full PNS points, which I believe is 99 because they don't give out any 100's, is to stay out of trouble. Of course you should try to do as well academically as you can because that is probably the next biggest thing they look at. Don't worry if you're not the most stellar performer during PT. Make sure you pass your PRT's and exhibit a good attitude during Batallion PT sessions. I think that the only time the CO will take into consideration when assigning his points is the last semester or two you have been there. So try to do your best the spring of your junior year and the fall of your senior year.
That being said, many people ask the question of what they need to score on the ASTB to be considered for flight school. I think you shouldn't worry about minimums. You should put some effort into studying for it and try to get the maximum score. The test is not hard, it isn't the SAT or the ACT, and you can take it again if you screw up. Now the harder question is, what score should you get before you are comfortable with submitting to the board. That's only because whatever you score last is the one that counts. Just get the 9/9/9 and be done with it.