After finishing the steps for GTA V Online Beginners you can still get more money by doing simple things.
Heists are a good way to gather a lot of money in short amounts of time.
Users with the criminal enterprise starterpack should have access to a free money laundery too.
After gathering enoug money, buy a nightclub, the cheapest one is on Elysian Island.
With a nightclub you can later buy a terrorbyte and with this a cheaper oppressor mk2 which is very usefull for preparations. This is the part that takes the most time, you have only limited sources to gather money but believe us, after the oppressor you only have to use the motorcycle club one more time!
The tipps for GTA V Advanced ones are in another post. Have fun!