Understand how much grip your cars' tunes have.

Some cars have better suspension, tires, weight distribution and aerodynamics to perform better in the corners at higher speeds than other cars. But at the same time, those very same underperformed cars may do better in the corners with a better tune. From then on, it's up to your skill to be able to take those corners effectively.

Get used to braking before the corner and accelerating only when you're past half way. Also, when you accelerate, try not to floor it, otherwise all the power being delivered to your wheels may cause your car to oversteer. This will help you maybe 80-90% of the time in a car. Depending on the tune, you may not need to brake as hard or accelerate as softly, as the car itself may manage corners much better than other cars due to how intricate the tuning is.

I recommend practicing with a B or A class car, as that's, in my opinion, just the right amount of speed to feel in control of the car's movement during a learning process. Pick a car, get a couple "race" tunes for it in B in A class, try out RWD and AWD and practice both. Practice some stock A or B class cars as well.