I agree with Cobra. The easy part is learning each plane's strengths and weaknesses, the hard part is getting everything together in your head so you know what to do, and when to do it and you do it with out stopping to think "oh I should do xxx". The plane you are in at the moment is important, but as he said, they are all similar in so much as you dont want to do needlessly dumb things (I'm still working on that part myself).
For example, all too often I am impatient and I fly straight to the fight, I dont take a second to anylize whats going on. Then when I get there, I have not got a plan to get out if I need to. And to top it all off, I regularly disregard his very good advice not to turn more than 90 deg.
The only thing I would differ slightly from what Cobra said is I think aggressiveness is key no matter what you fly. Do something they dont expect, like instead of zooming on a BnZ pass in a P-47, blow some speed, yank around and get them while they are thinking of what to do. Lots of times you can kill them while they try to decide how to counter a move they were not ready for. This can leave you high and dry in a bad situation though (and it happens to me) so thats not for everyone.
You should pick your fights, not let the enemy pick them for you, and always watch for someone trying to saddle you while you are killing their buddy, but once you decide to go for the kill, GO FOR THE KILL, dont hold back.