Here's what I've picked up so far:
1. Look before you leap. Get a good idea of how many planes are around and their relative motions before you dive in. Know which types and what their capabilities are. Check six.
2. Make sure you come up for air. Get clear after an attack, successful or otherwise, climb out if you can, look around and assess the situation before you go back in. Check six.
3. Sometimes getting clear means running far away from the fight. This is not cowardice. This is tactics.
4. If you're like me you have a voice inside your head (mine kinda sounds like my primary trainer guy, Morfiend) that tells you it's time to get out. Listen to that voice.
5. Greed kills. Don't get kill happy. The longer you stay in, the better your chances for getting shot down.
6. Check six.
7. If you're concerned about landing kills, never engage when outnumbered, never engage planes with superior altitude, never fly through ack. There are times when you may want or need to ignore these rules (base defense, or just for the heck of it). If that is the case, fly as aggressively as you can and drop as many as you can before they get you.
Regarding the planes:
The 38 is a difficult plane to master and you should talk to the experts before you fly it.
The F4U 1A is my favorite hog for furballing. It's biggest problem is that it can't climb very well, which makes it hard to regain energy in the middle of a furball. You really need to get as much alt as you can before engaging, and you will have to learn to exit the fight while you still have the alt or speed to do so. Plus, you have to learn how to throw the flaps out on turns and loops. Think of the hog as a long-lasting battery that takes forever to recharge. It doesn't bleed off energy quickly, but there's no easy way to get it back once it's gone.
The P51 is probably the easiest of the planes you've picked, but there are some traps that newbies fall into. You don't want to try a steep climb while exiting the furball...a lot of planes can catch you in the first part of the climb. A zeke got me that way, and 109k4's, FW's, Ki-84 and Spit sixteens can stay with you in a climb pretty easily. Go flat out to get some distance before you climb out. Don't think your speed makes you invincible. La7's, Doras and Tempests can give a Pony a run for it's money, and several planes have the acceleration to catch you in a short sprint. Don't stay too long in the furball. Ponies are very high on the "kill it first" list and you will attract a lot of attention the longer you stay in.
These are the opinions of a relative newbie. Others may know better.