Forget about money. Leveling up fast IMO is much harder to get done than earning money.
So when Double RP/Cash weekends come out this is how you take advantage of the system.
All these methods require two players willing to work together and don't care about silly things like K/D ratio.
I'll break them down by game type.
Capture (As of 1.15)
Find or Create a capture in an area with a predictable spawn area. Eg. Racetrack / School Ball Field.
Make the spawn areas right next to each other and as small as possible.
Set the team vehicle to some vehicle with little armor. Eg Motorcycle,Golf Cart,Dune Buggy
Set Score to 8. And Put a Time limit to like 20 minutes. Capture sometimes bug and the bags don't spawn.
Youtube bums only show you have to get piss poor ways of getting mass amounts of RP by telling you to end the capture by getting the bags really fast. Their method just allows you to get about 2000 RP (1000 normal) per session.
They don't bother to take the time to exploit killing.
So what you do is between you and your friend you figure out who's going to get RP first. Once you determine that this is how you proceed.
1) Start shooting your friend. If you pick a gun you haven't unlocked Awards for even better.
2) When your friend dies. Look where they spawn. Get near there. Kill again. When they respawn kill them again and eventually you won't have to really move and they will spawn fairly close or in the same location.
2B) The friend being killed should be pressing the respawn button to speed it up.
3) Kill until you get no more RP being earned.
4) Switch roles. Repeating 1-3
5) When that is done Score to end the game.
How this work is that is uses the Killstreak multiplier. So on your 15th kill or so its at 2.5X and its all gravy kills from there. 2.5 x 140 = 350 RP for lets say under level 50 2.5 X 500 RP (I think) for above level 80 = 1250RP per kill (Might be 625 as i haven't check recently with a high level player).
So Lower level players get lower amounts of RP. Higher levels 80+ Get more RP per kill.
6) I learned it is RP capped. So higher level players need less kills. A level 60 character needs about 41 kills while above 100 needs only 21.
Additional Capture notes. NPC players that can be set to be Actors. Hookers, Etc. If you kill them you get 50 RP per kill. Up to about 20 kills. Maybe 40 kills during double weekends. So thats about 1000 RP.
And don't mix it with the kill trading method above because it just gets messy and slows you down.
Deathmatch. (As of 1.15)
Design or Find an Asshole Map. Basically the respawn zone will be a pure killzone except for the guy with the weapon.
Same Method as the kill trade method. Just the respawn location isn't as easy to kill people as fast. And you're looking for Victims rather then friends. This is the Asshole method which requires you to use an Asshole map such as your 5219081720918095218092158091280952982 RP and $$$$$2184098121248921409842109 and if it has the work HAX or Guaranteed you get an extra cookie. The Kill streak limit is higher. But if you're working with a friend it is much slower.
It is a Victim map.
Races (As of 1.15)
SOLO races are Doubled. Normally you get 3000 RP for every 4 minute race max for high level players (2100 Level 64ish).
So 6000 for high level players.
Armored Car (As of 1.15)
There is a respawn glitch. This method is probably the fastest while it is available. Requires two players.
You earn enough RP for about 10 levels in about an hour for levels under 70. Requires a friend to sit in an apartment though.