Start at the car meet with some test track laps since it's pretty reliable for points, and you'll get bonus rp for beating your previous times. Running client jobs from the autoshop is solid too, with deliveries giving you 150 and finale missions paying out around 600 when completed. Maybe interesting, wearing car meet clothing while there increases what you earn.

Keep an eye on the official rockstar newswire for double and triple point events, those are definitely worth jumping on when they show up. If you're looking for something more passive, you can set up at the test track with your controller secured, and it'll keep giving you points while you do other stuff. Once you hit rank 12, crate drops become available and they're pretty decent, usually 3000 to 5000 per crate when you take out the guards.

Good to know, test drives and drag races reset daily, so you can't spam those forever. And while the passive method at the car meet works, just know the exact points per minute might vary a bit. Best approach is probably mixing these up, focusing on whatever's got bonus points that week, and filling in with car meet stuff when you need a break from the grind.