This achievement isn't THAT hard, though I do have a few tips.
STICK TO COVER!
Seriously it'll save your life more then once.
USE YOUR EQUIPMENT
Whenever you can use a sonar grenade, flash bang, frag or whatever other gadget you have up your sleeve, also don't forget to use your vision gadget, be it night vision, magnetic view or something els.
THINK
There are MANY situations where I could clear an entire section of enemies just by using my drone and thinking about what would happen. Main thing here is make sure the enemy don't see the bodies. Learn their paths, see what way they're facing and take them out.
TAKE YOUR TIME
Even though this game is focused quite a lot more on action then strategy then the previous parts, it doesn't hurt to go slow at times. Take in the terrain, take in your enemy.
USE THE RB BUTTON WHEN ENGAGED
This helped me out more then once. Just like tagging enemies for a quick synced shot, you can tag enemies when engaged. This will focus the fire of your squad to that enemy. You are able to tag up to 4, but you'll find if you have a good vantage point over the battle, your squad can be quite effective in taking them out, so keep on tagging when you get the chance.
CHOOSE YOUR WEAPON
Of course they give you your weapons at the start of the mission, but get a feel for one, don't be afraid to switch these out. Though another tip, keep it in the same section of weapons. For instance if they say a LMG would be useful don't take a sniper rifle. Other then that equip your weapon with what you find working well. I often added a laser sight to my weapon, it increases control and gives you a visual aid when aiming.
USE YOUR DRONE
Deploy your drone, let it hoover over the enemy, when tapping LB you'll go back to your character, while the drone will remain in air. The drone will send the orange outlines (when in contact) or red (when engaged) of the enemy positions, much like a sensor grenade.
JUST PLAY
Okay it's a game, so just play it. Be cautious of your next step be one step ahead of the enemy. Knowing is winning. Not sure where the enemy is? Find them before they find you. Crouch and use optical camo. Tag even though you're not gonna take them out just yet, it helps to see them.
DON'T STAY OUT OF COVER FOR TOO LONG
Trust me, you'll get your ass shot off. Tag 'em and bag 'em. Stick to your cover, tag them while in cover or peek out, then hit them with bursts, don't stay up or out too long, 3 or 4 shots are enough to take you out and there were a few times I didn't really notice how bad my health was and I took a dive.
I've completed the campaign without much difficulty even on Elite, yet there were a few sections that really frustrated me for doing over and over and over before I got it right, but learn from your mistakes. Don't take the same cover when you were shot there.
I think that's all I can give for you guys to help you with this achievement, now go out there and kick some ass!