I'm an wannabe amateur boxer, and am interested in gaining muscle without putting on much weight.
How do I do this?
Would I just eat only enough to maintain weight and not add 'extra' calories? I weigh 155 lbs.
Well, if you lose some bodyfat you can afford to gain some muscle.
But don't you mean that you want to gain strength without gaining weight?
Low reps and maintenance eating.
Keep an eye on those scales though. If you don't want to move up a weight division you may have to really dial your diet in to lose fat in order to stay under.
Gain Muscle without gaining weight?!
I agree with the posts above. If you can loose bodyfat, you can afford to gain muscle without changing your weight. Other than that I don't think that is possible. Muscle has to weigh something.
you'd have to lose fat and gain an equal amount of muscle at the same time. Not exactly the easiest thing to do, but presumably if you get your diet dialed in 100% its possible.
look into a carb cycling diet, it is a very effective method for your goals