Big bird cheat:
If you testfly the Spitfire in the museum, go out and drop both 500 lb. bombs and shoot away almost all of your ammo (leave about 9 rounds) then hit CTRL-A-E to shut down the engines. It will turn your plane into a big bird with a huge bomb under your belly. (It may take a few times but it does work.)

The Dynamic Mission Editor
Hit CTRL-ALT-Y while in a mission to access the Dynamic Mission Editor.

Tip 1:
Turn collisions off in your options menus. This should allow a few of your wingmen to land alive.

Tip 2:
Computer pilots usually push their fighters to the edge of the envelope but stop short of blackout or redout maneuvers. This gives you an edge in the desperation maneuver category, but don't push it to the point where you lose consciousness completely.

Tip 3:
For maximum dogfighting advantage, play with the virtual cockpit and the targeting arrow on. It's not realistic, but it gives you maximum situational awareness.