First i thought this achievement hard as f*ck, but i had to realize i was wrong. There are a few smart tips how you can easily do it. of course under easily i mean it's depends on the player how good is he in this game.
- First of all, know the story. Play through the game first on Normal difficulty.
- Reach Elite rank. To do this, complete the A.C.Es on the Terrorist Hunt maps on Realistic difficulty to know the AI better. Try to make a tactics in your head, how to beat the terrorists.
- Equip the best protector armor. I suggest you the Hurricane one. Use the Tactic Shield and the AK-47 with sniper scope and semi fire mode. It's much accurate if you fireing 1 bullet and DON'T use suppressor!
- Always move in small steps. Send your teammates first and if you think it's clear, go ahead. Don't worry. Your temmates are pretty smart and they will do the dirty work instead of you. Just don't send them into the fireline!
- Always use the Shield! It's block a lot of bullets and you won't die because 1 shot.
- Lure the enemies out! Use smoke grenades, fire everything with your pistol to make sure there are any enemies inside. Listen them, and watch out for footsteps!
- Use the thermal google. Believe me, it's much easier to see your enemies in a big room if you get used to it.
- Always tag 2 enemies with the LB button cause 2 reasons: First, you will see where is he hiding and second, your teammates will kill him instead of you, and you can keep focusing to the other bad guys.
- Use the snake cam before you enter to a room. WARNING! It's not working while you carrying the Shield in your hand!
I hope i could help you with these informations, and you can unlock this achievement easier with these advices. :)