Guide will update regularly weekends with the addition of new methods, to submit methods pm me.
It isn't necessary to max out commendations past Onyx aside from satisfaction, no cR will be rewarded at that point. To check what the requirements for each commendations are click here and for credit value here.

All campaign farming techniques should have scoring on and iron should never be turned on.
Farming works best on live so turn it on and don't be afraid to show off the progress.I'm serious
For the bright eggs in the crowd resetting challenges and commendations known to you as "unplugging your ethernet cable." is a bannable offense
Posted by: Condas Egera
When you complete an action in campaign you receive a set number of cr for each commendation involved. When those commendations reach silver the cr per action is removed. People know you receive less every time but this is why.
For instance, that cut scene method involves 2. One yields 150, the other 50. This is why it goes from 200 to 50 than 0.
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
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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 and if corvette isn't your style try checking this video out for a quick step by step on Holdout.
TacoHalo: Your kill is my kill at least with the AIs it is, a perfect collection of teamwork founded by no other than TacoHalo himself. Load up Long Night of Silence from mission start(yes the space level), no skulls, on normal. Now storm the beaches. Kill everything in your path and follow the shore till you hit the pier where a dropship will leave a nice wraith for you. Take out the gunner and jump in the turret to make the elite pop out of the drivers seat, after he gets out kill him too, this is to make sure that the wraith is for the most part damage free. Take the wraith back to the beach and boost around the rocks to go up to the facility and proceed to the sandbags and clear the area till you get the checkpoint and turn around facing the beach to get another checkpoint and whether or not you want one a marine will or should have already taken the position of the turret. Just let your AI buddy take out the covenant to get the following commendantions:
Leadership Element- Kill a leader-class enemy
Spec Ops- Kill a specialist-class enemy
War Machine-Kill with your vehicle
Cannon Fodder-Kill an infantry-class enemy
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Notes: I hadn't even tried the method and when first told about it thought it was stupid and immediately dismissed it and others followed, but one brave soul tried it and with great satisfaction, according to Pixel Push3r this method averages out to 4 kills a covie and even with dying the method reloads you back to the checkpoint so it naturally becomes a safe easy ride that can be done for the times where you just need a break and sleep in between the tough stuff, for a better retelling go here.
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.
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 to activate the cutscene. Almost 3-4 second after you push the button press start and click "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
Demon-complete a level
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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.

Online boosting lobbies*NEW*:
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. Resetting challenges to continually redo them is not farming, it's bannable.

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 AND THE RECESSION OF Cr FROM COMMENDATION, SO PLAY SMART DON'T CHEAT.

If you know of any other methods post as much information on them as possible.
I'll update the thread as often as possible with the addition of various other farming techniques.