Feint high (just out of range) to get his head pulling back (flick your jab up at his forehead). Then close the distance fast, fire/slide in underneath (shoulders lower than his) and stick him with a stiff jab in the middle of his chest/collar bone (stand him up). Put a body on him and start ripping hard body shots, once he steps back or covers up, turn him (pivot or step laterally), rinse n repeat! Where you don't want to be is in that 50/50 range, that's what he wants. Be just out of range, get his head pulling back (feint high, jab gloves, etc) and then close the distance fast and attack him while he's resetting. If you stick that jab in his chest on your way in, it'll freeze him up, let you get underneath and hammer him in the body. Keep up the pressure as long as you can stay underneath him, once he get's back to that 50/50 position, turn (pivot) or step off and repeat or reset just out of his range (in-out).