Remember to always brake in a straight line as you prepare for the upcoming turn. If you try to brake while making a turn, it will probably skid and take damage from crashing into the course barrier or any other obstacle on the course. Also, instead of holding down the brake key, always try to tap the brake in short intervals. This will prevent you from entering a slide (since there is no ABS in the game) and losing speed as you enter the turn.
Use the mini-map on the screen to judge the sharpness of upcoming turns. There are various kinds of turns within the game, from sharp 90 degree turns to small gradual turns. The racing line must be followed throughout each turn to avoid losing speed and crashing into the barrier around the track. The racing line is the best path through the turn that will give you the most speed as you exit the turn. Remember to hold the inside line through the turn. If any turns are combined into one turn, just use the techniques given for each turn and combine them together (for example, the S-Turn, is basically just two gradual turns placed one after another).