What Dagger said is correct however you will find it much easier to see the representation of the seeker head, this will let you learn when and when not to fire. When you call up your heaters (AIM 9's) press D on the keyboard to Enter the 'dogfight' preset.
This will auto switch your MFD's and change your HUD to decluttered mode, ready for a knife fight. You can also load the virtual seeker head onto the pilots 'helmet' (uncage the missle) so if you're using padlock or trackIR you'll see the same virtual seekerhead wherever you look. I think thats CTRL+U, but double check your options.
On a seperate note, if your joystick has enough buttons you should lock and breaklock so you can perform these actions while using your airbreaks/flaps incrementally and can focus 100% on the kill.
Hope this helps,
Preach
PS
Press 'C' to cancel dogfight mode and return to the last setup you had. Its also 'M' for the slammer preset setup, and to return to NAV mode I believe (double check your controls) its RightCTRL+ 'Del' on the keypad.
Preach