Aim for the balls.
nah. I am not going to be doing any hits in the croch area, or poking in the eyes. I'm going to try and win this fair and square, even if it means getting my ass handed to me.
Go for the jaw, not the head.
The jaw is a very brittle bone in most people. A good strong hit will make them think twice, put a person on their ass, or break the jaw. Otherwise, an upper cut cut below the ribs. This interupts the diaphram, making one lose their breath, possibly winding them. Not to mention, lots of soft tissue. A kick to the back of the knee will put a person down, and there are arm holds that can break the without much force.
Also, as odd as it sounds, hit the ears with both fists at the same time. It's disorienting and it hurts like hell. In some people, there is a nerve point between the shoulder and the neck, that when pinched, will weaken a person but it is extremely temporary and it doesn't work if they're relatively muscular in the shoulder area.
My MO when fighting is to disable my opponent. So, nothing wrong with "sitting" on your opponent if it means you've disabled his ability to harm you. Whether you take advantage of that is completely up to you.
Also, I would call the cops. Regardless of whether or not you started it, the fact that he felt it necessary to come to your house to take care of it means he's got a few screws loose. I.e. He's a violent person. He may, escalate the situation.