Source: http://gtaglitch.com/rp-afk-police-helipad-10434-rphour/
This glitch takes advantage of a place in the game where you automatically get 2 wanted stars, but also automatically lose and regain them. (giving you RP every time you lose them)
Once you start this glitch, you can leave it up and running for as long as you want to. (I personally let it run for 5 days)
Just remember that if you’re planning to do it for a long amount of time: make sure to plug your controller into the usb port.
[list type=decimal]
[*]Start an invite only session (in Singleplayer, select Online -> Play GTA Online -> Invite Only Session)
[*]Get a helicopter from somewhere and fly to this location:
[*]Land on the helipad (if the police chopper is already on the helipad, just land next to it)
[*]Get out of the helicopter and stand next to the door of the small brick building (you will now have 2 wanted stars)
[*]With a rubber band, force the right analog stick like this: (to prevent you from getting idle-kicked)
[/list] That’s it! You can run this as long as you want.

This glitch takes advantage of a place in the game where you automatically get 2 wanted stars, but also automatically lose and regain them. (giving you RP every time you lose them)
Once you start this glitch, you can leave it up and running for as long as you want to. (I personally let it run for 5 days)
Just remember that if you’re planning to do it for a long amount of time: make sure to plug your controller into the usb port.
[list type=decimal]
[*]Start an invite only session (in Singleplayer, select Online -> Play GTA Online -> Invite Only Session)
[*]Get a helicopter from somewhere and fly to this location:

[*]Land on the helipad (if the police chopper is already on the helipad, just land next to it)

[*]Get out of the helicopter and stand next to the door of the small brick building (you will now have 2 wanted stars)

[*]With a rubber band, force the right analog stick like this: (to prevent you from getting idle-kicked)

[/list] That’s it! You can run this as long as you want.
Rank | RP for next rank | Time to level |
1 | 800 | 5m |
11 | 4500 | 26m |
21 | 8200 | 48m |
31 | 11200 | 1h 05m |
41 | 14100 | 1h 21m |
51 | 16800 | 1h 37m |
61 | 19300 | 1h 51m |
71 | 21900 | 2h 06m |
81 | 24400 | 2h 21m |
91 | 26800 | 2h 35m |
101 | 28650 | 2h 45m |
111 | 29150 | 2h 48m |
121 | 29600 | 2h 51m |