Arts recommendation is good. In additional, get your bow in position. Then pull back and hold for 5 seconds, let up (bow arm still up) and immediately draw again and hold for another 5 seconds. Do five sets of these with as many reps as you can handle. You'll eventually want 10 reps per set and 5 sets total.
Don't try to make increases too fast, you'll want near to perfect form when you do these. You could also face posible strains which could also set you back by trying to get where you want too fast. Slow but steady climb is what you want.
In addition make sure that you warm up and stretch for at least 10-15 minutes before and after the these excercises.
I'd also recommend shooting with a form master for a while instead of target practice.