[SmartBastard]

Oversteer:
I guess it's pretty clear that you should counter steer. BUT you gonna have to be careful, because when you get the traction back, which happens quickly when you go off the throttle, and you don't correct the steering quickly enough back, you will spin out in the opposite way without much chance to hold it. Our car has a short wheel base which only makes it easier to spin out. It's all about training, therefor I plan to do skid pad training in near future.



Understeer:
You'll have to allow the car to get the traction back by turning the steering wheel back out of the turn (and therefor running wider in the turn) and turn back in again when the traction is regained. If you keep turning into the corner you'll actually make it worse.
If you have enough space you can try to "cure" the understeer my power and trying to put the car into oversteer. This should be first trained in save environment and not be tested on the track with other cars anywhere near you.