And: would it be wiser to focus on higher rep, but lower difficulty? such as raised pushups off a bench or something similar, or should i be foced on lower rep, high difficulty such as weighted/inverted pushups?

I am training to join the military, and I am having problems with pushups. I have been working hard for the past 3 months training to increase pushups, pullups, situps, running, etc. and I can't no matter what techniques I use increase body weight calisthenic exercises. I can do about 25 pushups, an...