Combat is inevitable in D&D, and when you play with miniatures, the battles can be a tad elaborate. Knowing the rudiments of battlefield tactics can mean the difference between an easy fight and defeat. Under the right circumstances, if they have control of the battlefield, a group of kobolds can defeat a high level party. I've never read Sun Tzu, and i'm no Captain America, but here are a few basic tips. As with everything in this series, most of these things will seem obvious. The "a-ha" factor is in realizing that these things matter in D&D.
Choose your opponent
Say you come across a powerful opponent accompanied by a group of weaker lackeys. Does it make more sense to ignore the lackeys and head straight for the big boss, or to clear out the lackeys first so you can then fight the boss uninterrupted, or to split your party up to take care of both simultaneously? The answer is dictated by circumstances and in truth there is no "right" answer, but the key is to have a strategy. Otherwise your opponents will decide for you in the way most favorable to them.
If things aren't working out, consider switching opponents mid-battle. This could surprise your enemies and also change the odds on a fight that was too evenly matched.
Notice what your opponents try to do and play to your own abilities. If you're fighting a group that contains a wizard and some fighters, and the fighters are doing everything they can to keep you busy while the wizard lurks in the background, they may be buying time for him to cast a particularly nasty spell. If you can't get around the fighters with brute force, is there something else your character can do that might work? A thief can fade back and try to sneak around, an archer could shoot over their heads, etc. But don't let your enemies decide your opponents for you.
Choose your battlefield
Whenever possible, get your enemies out of the area they have prepared and planned to fight in, and get them into one of your choosing. If you're trying to storm a castle this might not be possible, but if you're fighting a dumb Hill Giant who is standing in a field full of boulders that he's been hurling at you, lure him into the woods where he won't have as much ammo or room to maneuver. In a dungeon, maybe you can taunt your opponents and get them to chase you back into the area where your thief is waiting behind a door to backstab. When you camp for the night in dangerous territory, pick a spot that is easy to defend. When faced with a random fork in a dungeon corridor, consider what the advantages and disadvantages of each route would be in a fight.
This is all about teamwork. When you first approach an opponent, they turn to face you, regardless of what direction they were originally facing (unless you have skills or powers that make you extra sneaky). But when you are engaged in fighting an opponent, they can't turn to face your teammate approaching them from the other side. Flanking an opponent gets you a +1 on your rolls, and if you're on the correct side it also means they can't use a shield to defend themselves from your attack. Attacking from the back gets you a +2 (+4 if you are thief). So when possible it's good to work in pairs or teams to take out your opponents, even if it means leaving other opponents temporarily unengaged.
Wherever you wind up fighting, try to move towards areas that you can use to enhance your defensive position. Walls, hedges, piles of rubbles, etc., all give you place to duck under to avoid arrow attacks, hinder enemy movement, and possibly even give you a place to hide or rest during a battle.
It's harder to fight up a hill than defend a hill from the top. It's easier to pick people off with arrows when you're up on the castle wall.
A note about alignments and intelligence.
Obviously, your character's personality is going to affect how they act on the battlefield. We've all seen this sort of scenario: Wolverine (CG) charges headfirst into battle while Cyclops (LG) ineffectually shouts Danger Room training maneuvers in the background. This sort of conflict between characters makes for good role playing, but remember that Wolverine has a healing factor and knows what he can handle. No player, unless they are incredibly stupid (int or wis under 6), should act against their own self interest for the sake of staying in character. Even Conan, a kinda dumb chaotic barbarian, was pretty crafty when it came time to fight.
The main point, as always, is to think it out and not get stuck in a routine. Every battle you wind up in will be unique in some way. The important thing is realizing what is different and using it to your advantage.
You know, i have to believe that if Captain America did exist, he would beat the crap out of Donald Rumsfeld.
After seeing this picture, I'm on Iron Man's side.
Remember when I made those rat flank steaks? that was some good flanking!