Force = mass x acceleration.
Get your body behind you, will you be fighting with weights in your hands, NO, learn to pivot your body in the direction of your strike.
Bag work, do rounds on the bag, keep your guard up, always, alternate your bag work with 1 light and fast and 1 heavy, use a cooking clock for timing, light, rest, heavy, rest, light, rest, ect, keep going until you cannot hold your arms up, then just do light combos.
Train full body workouts, low weight high reps, lots of rest/sleep.
Take hits, its all well and good having six packs and training hard but if you dont learn to take hits you will be on your arse in 5 seconds.
Ive seen plenty of pretty boys with abs and shoulders go straight down on their arse fighting overweight guys who can take a hit..
Swimming will help develop your O2, and it is low impact, its good for recovery and fitness.
The main tip is dont get injured, always warm up.