how do i fight

i have never been in this position before but how do i fight?

Don't get in a fight.
If you want to defend yourself, have a self-defense weapon, and talk yourself out of fights, or run away if you can.

If you fight, strike first and hard, aim for the balls, throw things at his eyes, and once he his down, keep kicking (not punching, hard to get up if somebody comes) until you are more than 100% sure he won't be able get up. Stomping his fingers and breaking his limbs in life-threatening situations.

Do not ever try to have an honorable fight. If you really have to fight, do anything you can to win.