This can be very simple.

Primarily lots of sparing and hitting the heavy bag. Secondary anything that gets your lungs working real hard (fast jumping excercises, sprints,soccer,basketball) lots and lots of situps, pushups, bench press. Last but not least, a good coach and boxing books. Oh and lots and lots of prayer can help tremendously.

Better than weight lifting would be be a part time job such as bailing hay, ditch digging, tree service, or anything with fast lifting and throwing.

Also be dilligent and never give up. You will almost undoubtedly get beat up and humiliated at least once but three or five tears down the line you may very well be able to beat those who had beat you.