Midnight Club: Los Angeles

Here's a quick way: Equip ZONE at the garage, go into Arcade, and play the "Welcome to Hollywood" race with 1 Easiest AI and no traffic. If you drive well, you can get about 2 ZONE each race and the races are short.

If you wanna check your progress, you can do so in the garage. Also, don't let it fill up during the race for nothing. If you're only level 1, you can't store more than one use. So, as a rule of thumb, just use it as soon as you have it.

I found, while boosting the multiplayer cheevs, that whatever special ability I had equiped would rank up and pop the cheev after doing X amount of races even if I didn't use it during the race.

Go to the Garage and equip whatever ability you need to unlock. Find a buddy, go into an online private ranked lobby, I say ranked because that's where I did mine and I'm not sure if it matters, and just race each other until you pop your cheev.

My buddy and I both had this happen 2 separate times with 2 separate abilites, so it should work for all of them.