Balance is key in fighting. You want to stay on the balls of your feet, not on your heels. This way you will always be in punching position and able to respond quickly and move easier. It also allows you to rotate your feet generating punching power.
Keep your chin down and eyes up. This will protect you from getting hit in the soft spot which is the nose, eyes, and mouth. You want your opponent to hit you in the forehead region which is the hardest part of the head. More importantly keeping your chin tucked and hands up will protect you from getting knocked out.
Sit down on your punches. Use your legs and core to generate punching power. Slightly squat, drop your buttocks down, bend your legs while throwing power punches. Make sure you turn your waist and pivot your foot. Using your legs will make your punches more effective.
The right hand lead, left hook is a great weapon against and unconventional fighter (south paw) Position your front foot to the left and outside of your opponents front foot to avoid their power hand and make it easier to defend against their jab. Once you are at this angle you can deliver a powerful right hand, left hook combo then circle to the left to get out the way.