Gruntpacolypse:To do this go to Matchmaking-Firefight-Score Attack- then proceed to Gruntpacolypse on the desired map, the map i use is Corvette but you can pick your poison.
Commendations: Varying between maps you might be able to get more but credits that are full proof on all maps for this method are:
Longshot- Kill with a precision weapon (DMR)
Numbers Game-multikills
Methodical- any type of spree
Dome Inspector-Headshots
Target Practice- Kill infantry-class enemies
*Trigger Happy- Kill with small arms
--------------------------------------------------------------
Notes: You should average between 1000-1200 between games with getting additional Cr for the commendations completed within the round. the games will average at around 10 minutes so after a while it does get boring but, this will be played for longterm so should be saved last since other methods go faster.*adding the pistol every so often adds up for trigger happy thanks to Maytch
All campaign farming techniques should have scoring on

Flawless Cowboy: otherwise known as the cutscene glitch or cutscene farming. I've only done it on Winter Contingency a couple of times but i can say this as a fact, difficulty between legendary and heroic does nothing, skulls do nothing.
I'm not entirely sure but i believe the level has to be loaded from start. Play through the entire level, go to the room where you and Jorge will kill the zealot and then push the button. Almost 3-4 second after you push the button press start- save and quit. you get you Cr hen go back into the menu and resume game. as if god answered your prayers no playing just more Cr. as anyone would guess the affected commendation is:
Flawless Cowboy-complete a level on heroic or harder without dying
---------------------------------------------------------------
Notes: To ONYX the commendation you need to do this 300 times, the Cr for the commendation goes up but, for level completion it gradually goes down. It will proceed from 200 to 50 and most likely will gradually get lower, its one that isn't worth doing for too long, it take about 30 second to do it (because of loading) so anyone could do this in a quick 3 hour sitting and proceed to something greater.To put your hearts at ease


ONI Sword Base: I'm pretty sure this is the method that started all the controversy of Cr Farming. Now to start this level off let's add some skulls. "1.Cowbell" and "2.Thunderstorm" along with any additional desired skull should be used for this particular method.
1.big explosions
2.promote the covenant troops to higher ranks
When the level starts run up the right ramp, don't fight the elite and run pass him and drop to the grassy ledge so you can proceed around the corner(don't stay on the ledge there is this light thing that gets in the way and the grunts just pretty much destroy you, but after that it's ok to get back on the ledge). run down into the "barricade" and pick up the target locator, if the check point came already no big deal but if it didn't then proceed to get it and back up against the slanted door, wait for the check point to finish then aim for the cluster of covenant troops to get a barrage(10 or more) of kills. don't bother doing it again because you'll activate another checkpoint just reload to the previous check point and repeat, over and over again till you ONYX the following commendations:
Splash Damage- Kill an enemy with a heavy weapon
Walking Tank- Earn a multikill
Super Soldier- Earn any type of spree
Leadership Element- Kill a leader-class enemy
Spec Ops- Kill a specialist-class enemy
---------------------------------------------------------------
Notes: Aside from getting the checkpoint right if that's what you care about this method goes in varying speeds, some commendations will be taken out incredibly fast while others will be much slower. Splash Damage will obviously be taken out first but others like Spec Ops and Leadership Element will feel like an eternity and you'll probably not bother with it. The credits start of very good but eventually what was 80 turns to 50 turns to 30 turns to 20 turns to 12 turns to 6 and it just doesn't feel worth it when other methods are still going out there so it's best to get this done and out of the way so you can proceed to actually having fun.


Banshee: There are many places to kill the banshee or any other vehicular type covenant troop. I'll show you two that work as to my knowledge with the commendations being:
Right of Way-Destroy a vehicle
War Machine-Kill with your vehicle
1.Long Night Of Solace- Alpha Checkpoint Kill all the banshees leave just one so the checkpoint doesn't save, revert to the last checkpoint and repeat.
2.Pillar of Autumn-Raly Point Bravo the very last part where you take control of the big gun kill as many phantoms, spirits, and banshees. It's safe to assume if it flies you should kill it. kill as many things before the covenant cruiser shoots and revert to last checkpoint.
3.New Alexandria- just fly around and destroy, no checkpoints no limits just search and destroy the endless supply of banshee
--------------------------------------------------------------
Notes: Never tried this method yet but heard it's effective, for pillar of autumn i'm not sure if you'll get the war machine commendation but it seems like it'll go by pretty fast with Right of Way.


Nice Arm: On Winter Contingency run past everything to the jeep(get stickies) drive to where the spirit drops off a load of grunts (get out just before to activate the checkpoint), then get kills with one throw of the grenade and enjoy the benefits, revert to the last checkpoint and resume. This can also be done in Gruntpacolypse
Nice Arm-kill with a grenade
---------------------------------------------------------------
Challenges: Daily or Weekly, Challenges are always a good way to gain some Cr.Now while not really a "farming method". I find that the daily challenges are good for getting a boost, I don't really care for the weekly since the daily challenges can so far be equal or greater than the weekly. So before doing any of the real farming its best to get the challenges out of the way first.


Offline: I've noticed people playing forge or custom games for hours to come to threads and be "What the hell i played for 6 hours and only got 60 credits!!" All custom games and forge sessions average out to around 60 credits, there could be more but not by much. Also, not entirely sure but campaign may do the same thing offline.


KEEP IN MIND THAT Cr FARMING IS TIME CONSUMING AND SHOULD BE DONE WITH PREPARATION TO ACCOMMODATE VARYING FACTORS SUCH AS THE CURRENT Cr CAP OF 60,000

Please note: i do not take credit for this guide at all. All credit goes to SHOKAG3 from bungie.net