I will here attempt to be non style specific in discussing fight strategy. Simply remember to train your reflexes for the proper use of body mechanics. Prepare your mind for a self defense mindset, rather than hostility. Remember "zanshin" - remaining mind. This is your most powerful weapon. Prevention is better than cure!
When faced with a heavy handed puncher, his or her hand speed and upper body defenses may be hard to match or get past. In this case, timing and creativity are of high priority. In a street situation, you do not have time to memorize his or her habits. Neither do you get the benefit of watching fight tapes beforehand. Watch for openings in the attacks, and draw out your opponent for a timed hit. Don't forget use of body shifting; especially to the outside of the opponent, which will present you with a strategic advantage. This reduces his / her options by 50%. This will be easier or harder to do depending on the
attacker's training; such is hard to judge immediately, so it is instead better to take the initiative and/or counter-hit as quickly and efficiently as possible. Untrained punchers, however, tend to have a large amount of telegraphing (movements that signal a certain attack, not unlike "tells" in poker).
Against a kicker, remember that people are already on the brink of disaster on two feet, and taking another foot off the ground ruins balance even more. Also, a kick generally takes longer than a punch to reach its destination. Use this in conjunction with "stop hits" when you are at or just outside of the attacker's kicking range. Essentially, you will want to react to the opponent's starting movement as quickly as possible with a jamming technique or combination. Be extra careful when the attacker does manage to raise a kick. A well trained kicker can often change a kick's height or target before putting his or her foot down.
You must maintain a strong cover from which you can counter swiftly, and off-balance your opponent while their kicking foot is still traveling. Make an opportunity to close with the kicker, and reduce his or her options. Elbows and knees are particularly effective for striking away kicks, and use in close-up fighting. Use caution, however, if your attacker appears trained in a heavily body-conditioning oriented flavor of Muay Thai / Thaiboxing, Kyokushin karate, or the like. Counter striking to vital areas that cannot be conditioned (solar plexus and so forth) will be even more important in these cases.
Many fights end up hitting the ground. If you are not comfortable working from the ground, then maintain a solid fighting distance and avoid in-close fighting as much as possible. Adding to the danger of ground fighting is the possibility of more attackers arriving, glass on the ground, weapons, and your most immediate attacker being much heavier, as well as numerous other factors. A grappler will have methods of closing the fighting distance with you, and taking you out of the range from which many types of strikes can be thrown solidly. In this case, make well-timed use of elbows, knees, standing submissions, reversals, makeshift weapons, and other such anti-grappling maneuvers. Be especially careful not to over-extend your strikes, or leave them extended for long after delivery, against a seasoned grappler.
When faced with an attacker who you suspect has a weapon, you will, of course, have even more reason to seek means of escaping the situation other than hand to hand combat. It is possible that if you comply with your attacker, they will let you alone afterwards. However, do not always be quick to believe that he or she shares your belief system; they could very well harm or even kill you after getting what he / she wanted.
The attacker may also be on drugs such as PCP, which would make him or her very dangerous to deal with. Pain compliance may not work as well against such an assailant; move defensively while doing as much damage as possible. Use the environment even more so, such as getting free to run and throwing things in his / her path. Also be extra careful of weapons the attacker is wielding. If at close range, attempt to stop the weapon from even being drawn. If this is not possible, dodge an attack or jam it as your opponent comes at you. Control the wielding arm, and strike at your opponent with your free limbs, head butts, etc. until you can disarm or subdue. It's also very important not to get caught off guard with a handgun, which would put you at a severe disadvantage. In this case, use distraction or other methods to diffuse the situation, and disarm if necessary.
Overall, many attackers will concentrate on their "weapon" (striking, grappling, a weapon, sheer strength or numbers, etc). Your attacker may believe that he / she has something that guarantees success. There is no way anyone can plan ahead for all situations, however. You must instead constantly learn, as well as use strategy, adaptability, and heart to your advantage, in a fight or life itself.