The GTA Online racing scene is both lively and competitive, full of both the best and worst the game has to offer: dedicated racers with both skill and experience, as well as unruly newcomers who only popped in for the unlocks but have no actual interest in the sport.

If you're being left behind in the dust by the former or being constantly rammed off course by the latter, you could definitely use some pointers in the right direction. There is more to racing than mere stats, which is why a skilled driver in a mid-range car can still beat someone who has the best ride fully upgraded, but no skill to go with it.
The two techniques you need to master is redline starting and curb boosting. A fan of GTA Online and user of Reddit compiled a great set of tips to get the hang of both of these methods, which you can check out here.
Redline Starting
Firstly, one of the most crucial sections of each race is right at the beginning. Oftentimes it is your start that will decide whether you lead the race or fall back, and few players know how to get it just right. The part that everyone knows is that when "GO" flashes on the screen, hitting the accelerator at the right time gives you a bit of a boost.
What most people don't know is how to maximize this effect. Simply keeping the accelerator pressed down during the whole countdown will blow your speed boost. However if you rev up your engine, let go of the accelerator right before the "GO" prompt appears, then re-press is at the right moment, not only do you gain the normal boost, but the engine retains the bonus from revving it up as well. This should launch you ahead of those who simply hit the pedal upon seeing "GO".