I was wondering if anyone knew the best way to be able to do a certain amount of situps? I am going to basic training August 13th and if I can do 52 full situps then I will get promoted. I can currently do 32. What is the best way to strengthen your hip flexors because they play a big roll in full situps. Should I just do full situps like every other day and do 3 sets and do as many as I can in each set?

leg raises and sit-ups are really about the only two exercises that work the hip flexors specifically. Try somr weighted situps and leg raises. It will increase strength and make endurance better when doing the sit-ups unweighted.