One of the rules in driving taxi is to speed up because no one wants to be late on their meetings or whatever they need to do. Surely, they won't come back if they are dissapointed wiht your performance. You need to make sure that they come back and that is how you get a stable income from taxi.
Drive your taxi as fast as you can till you reach the finish line. The game has a time limit and you can't extend it, but you can get your car at high speed if you get the power-ups (speed). Aside from that, there are also other power-ups that would be useful for you.