1) To more quickly deposit any money you have made ( instead of going to an ATM ). Use the "Internet" on your Cell/ Mobile Phone and click on the "Money & Services" link at the top of the page.
Then click on "Maze Bank" ( your Bank in GTAO ) to deposit money remotely into your Bank Account. This will avoid any other players camping out near an ATM waiting to kill you and take your money.
Here's a quick video guide ~
2) Make sure that the first vehicle you steal is a good one. Because you only get 1 Free Car at the beginning of GTA Online ( with all the customizations free for it ).
3) Easy Early-Game Money - To earn money easily at the beginning of the game without alerting the police, steal a good common car in Vinewood. Then, go to Los Santos Customs and sell it to them ( you can sell stolen cars to LS Customs in GTAO ), although this will not work for Luxury Sports/ Super Cars. If you try to sell one of these to LS Customs, a text pop-up will appear saying that the car is too hot for them.
You will get around $9,000-$10,000 for a good common car ( which doesn't have too much damage ). Once they have paid you the money, I would advise going to an ATM or using "Maze Bank" on your phone to deposit the money into your Bank Account ( before another player tries to kill you ). You can repeat this as many times as desired.