Search Youtube for boom'n'zoom Il-2 videos.
Check out this guy's Dogfghts series for example
http://www.youtube.com/user/BigSilverHotdog
Turn off vulnerability, limited ammo and set some bombers in FMB 1500m below you for practice. Dive on them when you are right above them but not when you are behind them. Zoom after attack into the right position above them and repeat for 2 hours.