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).