I'd say that for the most part, don't spend your cash on supplements and instead spend it on good food. Stop eating sugars (esp. high fructose corn syrup) and you'll see a big increase. Get rid of all the fried crap, start munching on carrots instead of potato chips... If all that is too much, start making small changes- get rid of soda. switch to decaf. downgrade to 1% milk.
Oh, and I did this online program for pushups... (google 'hundred pushups') I did the initial program and kept increasing it incrementally. Because of my semi-crippledom, it took me nearly 12 weeks instead of the website's six, but after completing it and using their formula to increase strength, i'm up to 560 consecutive pushups.