Pimp Maria's and Andrea's ride to unlock Hari, Leon, and Alix as customers.
Pimp Hari's, Leon's, and Alix's ride to unlock Alyana, Jason, and Sandra as customers.
Pimp Alyana, Jason, and Sandra's rides to unlock Zeke, Na, and Jewels as customers.
Better score
Most of the time the kind of things in most need of pimping are usually body kits, paint jobs, and rims. Go for them first to get a better score.