Thanks all for the replies and help. I've now been able to shoot down my first enemy fighter, and many light and medium bombers. Couldn't have done it without you.
Edit: After this post, I shot down two more (LaGG-3s)! This place is good luck!
However, a few things still confuse me:
1.) For hard turns, if I have to make one, I usually throttle down to 0% briefly, as I've seen others do; I'm not sure exactly on the best timing, though -- I usually have it on 0% throttle for the first half, then go back up to 99/110% (usually) as I pull out of the turn. What should I be doing?
2.) In the 109/a BnZ fighter, what do I do after I blow past the enemy after trying a high angle off shot? I line up the shot, and whether I miss or not I usually find myself heading away from the enemy at some high angle; I then usually try to turn around to have another go, and get a LaGG or P-39 on my tail as a result. Should I be trying for altitude or a lot of separation before doing any turning after an attack run? Is my strategy totally wrong? (Except for bombers, I don't find myself directly behind a lot of enemy planes, so I live on a diet of high angle off shots.)
Edit: After shooting down the two fighters mentioned above, I think just not bleeding off any speed and attaining a wide separation before trying another run is the key. I'm avoiding hard turns (and turning fights) and using speed and altitude to set up shots/disengage. No flaps except combat flaps for particularly hard turns, throttle down for dives and turns and up to 110% sometimes, second-widest FOV: big improvements along with knowing what tactics (speed, altitude... gunnery practice!) to use with a fast but wide-turning fighter.
But if I'm getting anything wrong still please tell me -- I'm hardly an ace, even after my magnificent third fighter kill...
I definitely don't know what to do when an enemy is on my six: I assume, with LaGG-3s and P-39s, I'm gonna want to try to outrun or outclimb them, but how to avoid getting poured full of lead while I do this....
Edit 2: Well, those tactics didn't work at all against P-39s. Altitude and speed did alright, but I couldn't outrun them -- so when my diving ambush failed and I tried to disengage, I just wasted a lot of time (seems they can't quite catch me either). I tried again and got one while coming down from on high, and got a second one by engaging in a turning fight. (Then I got shot down by a Yak of some kind...) Either the 109 can maneuver better than the P-39 (I've heard this so, but I think at higher altitudes than I was at -- maybe not), or I just got lucky.
This game is getting extremely fun, though... I'm glad I stuck with it through the frustrating.