Do more pushups.
Go until you reach about 90%, then stop and rest in an altered front leaning rest position by either arching or sagging your back. Crank out some more then again stop and rest in an altered front leaning rest position. Continue for 2 minutes. Rest 2 minutes. Repeat 5 times.
Try doing numbered sets: 10 sets of 20, etc.
Try just staying in the front leaning rest position for a few minutes.
Try altered hand positions:
-hands close, arms graze your ribs with each rep: more triceps
-hands wide, position up toward shoulder level: more chest/shoulders
I find that if I place my hands about midway out and down level with just below the nipple line (upper arms angled down about 45 degrees) I am able to do more pushups. You'll notice if you bench this way you'll be stronger on the bench as well. So during the pushup you're not so much coming down to your chest so much as you are coming down to your sternum. Also angle your palms out a bit as well.
Alan