What rank are you? How much money do you already have? This is what I have been doing lately, currently rank 93, and I can pretty much gain 1 rank every 30-40 min.
"After hours and hours doing the "Coveted" mission (I think that to kill the enemies every time is a bit boring), I'm doing my quest for Rank 100 in another way:
* After getting about 1.750.000$ I've buyed a Buzzard helicopter and a Nemesis bike;
* Start the "Crystal Clear III" Mission (Host Mission, Rockstar Missions);
* Start the Mission and call the Mechanic to get you the Nemesis, after that call Merryweather and get the Buzzard;
* Run to your Nemesis, and drive to the Buzzard (that it's near, I'm just lazy to run everytime to the Heliport);
* Fly the Buzzard at a medium altitude (so if the Vagos fire, they can't hit you) and velocity to the 2 Meth Labs ahead, change the weapons to Missiles and rain death upon them with the Buzzard's auto-lock system; after that finish the 3rd Meth Lab in the same way;
Doing this you get 2000RP + 7000$ in about 3:00-3:30min each time (with restart and loading times). Note that after doing the mission a first time, the bike will be always near, the only thing you have to do is call the Buzzard and run to the bike and start the drill. "
Credit goes to Born Apophis.
Check out the thread - http://www.xboxachievements.com/foru...555998&page=11