Things that helped me to get better in the F-5: Be careful with your speed and dont pull too hard. Once you're slow, it's hard to regain that energy with a MiG on your six. Also with high AOA, use rudder to roll, that way you'll bleed less speed.
If you're up against AI, dont follow the enemy plane into the vertical. Youll just end up stalling. Instead follow him in lag pursuit, turn in the horizontal plane, and then roll in behind him as he comes down again.
I also set the flap settings to my Warthog throttle boat switch. Aft is set to flaps auto, forward is set to flaps up. That way I can easily switch between fast(er) acceleration vs. better turning performance.
If you're defensive, use the F-5s nice roll rate for a scissors maneuver and force him to overshoot. Theres a button for turning off the roll limitation on the stick, I bound that one too on my joystick.