Start a job as security worker by looking for a "securicar". The main goal is to pick up the valuable content from one of the local companies and bring it to the other place without getting robbed. The pickup and delivery spot will be marked on the minimap with red dots.
This job has a very good payout but comes with some risk as you might get robbed by other players. After being robbed you have one minute to kill the robber and take the money back to your truck.
The job can be done with more players so it's easier for you to deliver the cash while your team mates are protecting you.