more money

Doing odd jobs, etc. Also giving Stevie cars, should you have already completely his car thingmabobs.

You could kill people and take their money, or you could enter in a cheat. You can also do jobs like taxis and police jobs.

You can do jobs like paramedic and vigilante. You can also rob people but this is probably the slowest way to make money due to the amount of times you end up either fighting or running away from the police.

Kill peds
Sell the required cars to stevie, or random ones if you've done them all
Rob clothes stores
Do work for your friends

Do the jobs like the Paramedic, vigilante, cabbie, etc.
You should also do the car thing for Stevie, as you'll get cash. Sometimes the best way is to kill people then steal their money.

Kills civilians,that's the fun way

Or you can do taxi missions which are always fun

Kill people on the streets.

If you have a Buzzoka (dont know how to spell...but the rocket thing) then go down near Bruicies lockup and theres usualy some bank trucks goin around if you blow em up and take the money you WILL make between 500 and 1400$ per truck, and civilians is always fun to,
HOPE I HELPED, MaStEr!