1. Use airbrake!
I noticed that many players are using airbrake very rarely! THIS IS A BIG MISTAKE!
At speed above 400kph(250mph) the airbrake is much more effective than wheelbrake.

2. Use Airbrake when passing turns.
When you engage airbrake at half (the spoilers are engaged with angle of 45 degree) you have maximum downforce. So, with airbrake you can pass the turns at higher speed.

3. Use ABS!
You can enable ABS separately for front and rear axes.

4. Tune your traction computer
The car have autopilot that helps you to stay on road. You can change parameters of it and make controls
more fast or smooth. Double click on the right bottom button "Gyro" to open setting menu.

5. At the first time try to pass the track at low speed
Dont try to be a guru at first time. I want to tell you that only 2% of players passes the first turn. But those who able to learn before enabling uber afterburner, rocket booster and full throttle can reach the second turn (but will crash anyway!).
Try to feel the car, it is physically correct. When you understand this you could be a cool pilot and it would possible to you to pass the tracks at very high speed without crashes!

6. The ramps
This is your problem, I know. Uncontrolled turning just after take off could be caused by high speed and unaligned take-off.
Try to align the car to follow speed vector and ramp jump vector. If you have a non-zero beta angle (angle between speed vector and car axis vector, it could be non-zero when drifting or turning) you will get an uncontrolled turning when airborn. This is physically correct, watch the stunts on youtube where some crazy people are trying to jump at long distance on their cars.
You have an ability to control the roll axis in-air. Try to align before landing. Dont jump at high speed, you will die 99%.

1. Use rocket boosters on turns.
This is simple trick if you feeling that you are not fit into this turn and will smash your face into the nearest rock. Try to enable rocket boosters immediately. By this action you will add a huge thrust directed to the outside of the turn.

2. Switch off autopilot to do some stunts.
To do dangerous but the amazing stunts press "DisarmASC", "Handbrake" and turn left or right.
After the full turn release all buttons and try to stabilize the car.
You can do multiple turns. Simply try.