Some things I can't do, as the car is used for sprint racing in a low power to weight class, however for road use I do have 155/80/13 tyres.
Calibrated right foot
Removed all equipment from the interior. 1 seat, no carpet etc.
Air Dam (Not extending below floor height)
Running exhaust above flat floor or inside the car.
Moving air intake to area of stagnation.
Move fuel tank closer to fuel pump.