Follow this guide to earn good Cr in halo reach.

Game Type!


Ok for game type you will want to play SCORE ATTACK , Ok for people who dont know what score attack is, it is basically a one man firefight with a limited number of lives. But you get massive amounts of CR. I would suggest picking score attack of the choices of variants you get because you get more CR. Gruntpocolypse is easy but you don't get as much CR.

Strategy

I like to run around with my DMR and needle rifle spamming nades xD but you may not be like that so I will make this section for you.

One strategy is to camp and conserve ammo. Depending on the map this can be either easy or hard. On courtyard it's pretty easy. All you need to do is camp at the spawn doors on courtyard. Now on waterfront camping is harder and I would suggest running around. I'd say the best map to get CR on is corvette. It's nice for racking up multi-kills and headshots.

Another strategy is the suicide tactic which isn't that great due to the lack of lives in score attack. But anyway's this is simple, All you should do is run around and find a nice group of enemy's and rush into them and kill yourself with a grenade or any type of explosive. It will rack up a nice overkill or higher if you do it right. I would recommend holdout to do this tactic on as it is a nice and compact map with alot of enemy's grouped up.

My next tactic is the rusher tactic. You will run in groups spraying , praying , and spamming nades. That is a decent tactic if you know how to do it. I like to use a needler and have a needle rifle to back me up. A great map for this is also courtyard.If your not camping then rushing on courtyard works well.

My next strategy is one I like to call the "Shoot , Cover , Repeat Process" I call it that because that is literally what you would be doing. Taking cover then popping out to shoot and go back into cover. This strategy is good with precision weapons. I like to do this strategy on overlook, glacier , and beachhead. Those are some pretty good maps but you will die quick if you don't use cover.
Another strategy is the multi-snipe strategy that is used in sniper attack variant. To do this you go to a spot at the end of a map with cover and snipe all of the enemy's as they come across the map to you. If reinforcements are landing near you go to the opposite side. I use this on beachhead.
My last strategy is the "all out defense" strategy. This is used on crashsite game variant. What you have to do is go back to the generator you are defending and sit behind it and look out with your DMR. Now you have infinite ammo so keep this in mind. Keep behind there until you die or want to get a new weapon. If you want a new weapon i suggest doing that in between reinforcements to prevent death. Basically just camp and pop out to throw a grenade or shoot a group. My first game of crashsite i got a killionare with a grenade.


Outcome

If you were using this guide you should be getting some good score's. You can get score's as high as 2500 if you are good at this and a minimum of 750(est) if your not even that good by following this TuT. By using this you can level up very fast. I have gone from a warrant officer to a warrant officer grade 1 very fast by doing this. But here is my estimations of what you will get by gamemode.

Score Attack = 1000-2500 CR

Gruntpocolypse = 700-1250

Generator Defense = 800-2000

Sniper Attack = 800-1250

Crashsite = 750-1200

I do not take credit for this guide! Just posting to help.