My question is at 400- 600 on the enemy icon is he actually at 400-600?
0 - 99 = d0
100 - 299 = d200
300 - 499 = d400
500 - 699 = d600
700 - 899 = d800
900 - 999 = d1000
1000 - 1249 = d1.0K
1250 - 1749 = d1.5K
1750 - 2250 = d2.0K
To answer your main question: The best thing you can do to get better @ dogfighting is by getting someone better to show you. Could be a a trainer or just an experienced player - many of the best dogfighters in AH2 are more than willing to help other players.
The second best way (and the one that I went) is to film all your fights and examine afterwards what went right and what went wrong. If there's a film you find particularly notable, you may post it in Help & Training forum and ask for reviews.
A final note: It may be helpful to look at your stats to get a rough idea how you are doing and if you are getting any better... but forget about the rank numbers for now
