I lift about 3 times a week, how often should you increase the weight lifted for max results, and by how much?

Question

also, I don't have a bench so I can't do bench presses, but I do push ups, are there other muscles that bench presses work oout that push ups dont?

Answer 1

The weight is not the key, the reps are.

Start doing 8 reps for gain in size, when you can do 10 you are almost ready for more weight, when you can do 12, start adding weight, 5 lbs (+/- 2 Kg).

But who needs more weight, try doing the same reps with same weight, but... do them slower... believe me, is more effective than adding weight (to certain point of course).

All these is over the 3 series of 8 reps basis (for gain in size).