Time and time again I've heard noobs ask for tips and I never really know what to tell them. It seems to me you need both experience and practice. I realize some think those are one and the same but I consider them slightly different.
Experience is learning what you can and can't do and what you can and can't get away with.
Practice is actually going out and doing it. I've found even if I'm away from the game a couple days I need an hour or two to get back in the swing of things, so flying regularly is important.
If there was any one thing that I think greatly improved my game, it was finding the right plane. Not so much because of the plane, although the Nikki is my plane of choice now, but because it taught me to shoot in short bursts.
I started out in P51s and, back then, it would be all I could do to shoot one plane down with all the ammo I had. I'd just spray shots, wildly at times, hoping for a lucky hit. If I actually managed to get a kill, I'd have maybe 100 to 500 rounds left and would run for home since there'd be no way I figured I could get a kill with just that much ammo.
A squaddie recommended I try the Nikki. I was a bit nervous about only 400 rounds of canon ammo and I tried to conserve it. That got me in to taking better shots with better effect and lots more kills.
Now, although the Nikki is usually my plane of choice, I don't have a problem taking out planes with less ammo like the fm2 or p51b and I'll get multiple kills with them. I'd like to think I owe that to the Nikki.
I actually disagree with the one who suggested getting into furballs right away, at least right into the middle of them. You'll likely get shot down too quickly to learn anything. One on ones are good, or even hanging around outside of some dogfight and sneaking in and cherry picking (I know it's frowned upon by most, including me) will help you learn how to approach targets, and how to get away from them.
I think one of the mistakes I made earlier on was being too aggressive. I'd be the first one to charge the enemy and they'd usually eat me alive. Take your time and see what others are doing before flying blindly into a fight and getting your head handed to you on a platter like I always did.