Like a lot of new players, I am getting shot down regularly. I fly the P38L, and would like to stick to it rather than chasing the "win button" plane, if such a thing exists. Anyway I have a couple of questions:
1) What's the best way to improve your dogfighting skills? Practicing in the arena is the obvious choice, but flying for 15 mins just to get shot down as soon as you reach the flight is a very time consuming and frustrating way of going about it, especially since you get no feedback of what you did wrong.
2) Often I will be in the situation where the other aircraft has an alt advantage over me. Usually we will be heading towards each other, just the other guy is 2k above me or thereabouts. 99% of the time, the enemy plane with fly over me, then pull a split S to come down on my tail. Now basically there are 3 moves I might try in this situation: a) split S, b) immelman, or c) flat turn. However, no matter which move I pull, the enemy always ends up on my tail and I end up dead. Are there any tips for this situation? I am considering just running from any higher alt enemy fighters in future.
Er, that's it for now I guess. But any tips for improving would be gratefully received. 
d) Time a pull up so that he overshoots below you...an exchange of positions. Reversing an E advantage expeditiously is based on the principle of making him go nose down to the take the shot and ending up above him as many times as is nessecary for things to finally equal out.
Bandit barreling down on you:
Believe it or not, the more overtake he has on you, the easier your job is, and vis versa. The major defensive trick is to initiate a break turn at the right time, usually at least somewhat obliquely downwards. Try to get 90 degrees when he comes into firing range. If he pulls up and you don't have the speed to follow him up (you probably don't-yet), go on a path away from him. You can go straight and level, dive, or climb at high speed, depending your energy state. Try to stay at maneuvering speed. If he is tracking you for a shot, poing your wingtip at him, giving a narrow profile, and go up or down, depending on E level. The "out of plane jink" part as it is called will spoil most peoples shots, and if have the airspeed to jink with a pull up, he overshoots beneath, and you've done the reversing positions thing which will help cut down his speed overhead.
The P-38 is a pretty decent plane, and I would not discourage a new person from flying it. It seems worse than it is in a dogfight for two reasons: One, its planform makes a big target. Two, hordes of late-model Spits that do everything better and are very easy to fly. Okay, let me add a caveat: A plane with the P-38's speed, climb, turn and roll numbers would be a POS if it were single engined. However, the P-38 is NOT single engined. It has no net torque, so balls to the wall, almost no airspeed? No problem. Outstanding with the nose up, single engine jobs will run up against torque and flip over trying to pull the same maneuvers. The P-38 requires extensive flapwork to get the best out of it.
I'm going to disagree strongly with Agent here. I think turn performance is the easiest to use attribute in ACM and big stunter of a player's development in using geometry to gain the shot, rather than simply holding the stick back and listening to the stall horn until the bandit's tail is waxed. Pretty much a personal choice about how you use speed. You can use it to HO and go...or you can use it catch stuff and force fights, and disengage from the umpteen vs. you situations from which you will learn nothing except how lamely some people will strive to earn 1/10th of a kill. The P-51D would be an ideal primary trainer if its turning attributes were a little better...quite possibly it still is, because you can find other P-51s, Jugs, Typhoons, 190s, and other poor turners to fight. I may be burned at the stake for this, but I'm going to toss out the La-7...its a good but not uberturner, and it is fast enough to catch up and force a fight with just about anything. Just don't "Ho and go" in it, please. Its guns will force you to maneuver for the sort of close range, dead-easy shots that should be your bread and butter in any plane.
Oh yeah, one of your most important maneuvers in any plane is going to be chopping throttle and standing on the rudder. That is the only "air brake" most of these planes have. Remember when I said earlier that a bandit barreling down on you fast was easiest to avoid? Well, you are going to want to close to firing range expeditiously, but once you get there you want your closure rate to be reasonable so you have an easier shot. There is alot of talk about conserving your energy, and it has its place, but many times you will be far better off if you saddle up and kill that bandit NOW, before a second one comes in, instead of trying to conserve your energy while fighting the one and ending up fighting two at the same time.
