Note: These tactics are not to be used with lethality. They are to teach you what to guard on yourself and how to temporarily disable your opponent. Obeying local, state, and federal laws remains your responsibility. Don't use these to start a fight; they won't work for that anyway, and self-defense if a much less serious crime than assault and battery.
To date, the single most successful tactic for winning a fight is not to get into one in the first place.
There are certain parts of the body more vounerable and sensitive than others. Some you may already know; others may be a surprise. The most obvious and effective, on a man, is the testacles (more simply, his balls). Here, I would recomend a kick as it is often hard to get into a good position to take a shot with your fist; however, if you can, a punch is often just as effective and harder to counter. This, if you can get a solid shot in, will temporarily dissable your oponent, allowing you to tie him up, or, for good measure, give him another shot (or two) in the pills. He will recover, but not soon enough to chase you down before you can get yourself better prepared for his rather likely attempt at revenge. If you gave him a good solid one, it would probably be a few days before he can fully recover from you. If this place is not an option or just not your style, there are of course many other options.
Next, the diaphragm. Those of you familiar with human anatomy know that this is the muscle that controls breathing. Though most of it is protected by the rib cage, a portion is open to attack just below the sternum, where the two halves of the rib cage connect. You may want to feel this area out for yourself: where your stomach softens somewhat approx. one to two inches below the bone is your target. You should use an uppercut as opposed to a straight-on punch to get the best effect. If your attack is successful, the wind will be knocked out of your opponent. They will barely even be able to breathe much, hardly move at all, much less fight. This is very temporary, though; whatever you plan to do, do it fast. If you're not successful, watch for a shot to your own chest, which is usually left open during a close-range punch like this. An alternative to the same effect would be a heavy, blunt blow to the entire chest. A hard shot with a shovel or something similar would work.
Another spot to guard would be your neck; specificly, your wind pipe. Though it is a small area and relitively well guarded by your own chin, one could punch it and send you reeling. Even worse, it could collapse the cartilage rings that help it keep its shape, closing it down completely and tightly and, if you don't get medical attention SOON, permantly. Another thing to look for is what I call a "hook" chokehold. It is when, instead of a blunt hold around the entire neck, the fingers are specificly wrapped around the majority of the wind pipe. Speaking from experience, this is not a comfortable position in which to be held; however, speaking from even more experience, if you are the one holding, it quite a comfortable position indeed. You can calmly negotiate your captive's release however you want now, which I prefer over the blunt hold, as they are still able to talk fairly well.
Now, the tough stuff that doesn't really work as well. They are still more effective than a simple punch at a random location, however. First, the kidneys. They're on either side of your lower back, a few inches below the rib cage. The back of your foot in a roundhouse kick can make them piss red for a week, not to mention make them piss whatever color right away. In fact, it might even relax the rectal muscles--and that's never a good thing unless you've got some toilet paper handy. If you wanna try THAT one, aim a little lower and in the center, at the tailbone. No guarentees there, though. You'd probably have better luck with the brown noise.
Not a hands-on type person? Wussie. Still, there is a good, much simpler system for you. As soon as you get in a fight, run (ha-ha). I mean that, though. Run and get a weapon. A sturdy stick, a piece of pipe, a bit of a bar, whatever; nothing you can break with your own hands, nothing that goes higher than your shoulder from the ground up. If you're anticipating a fight, do so before hand. All the rules above apply still; just tailor your attack style to your weapon, you should be fine.
Of course, any feedback is quite welcome. Any mistakes I might have made here, or some things you think (know would be better) would work, let me know.