Well, this achievement is easily obtainable on Rookie difficulty, but feel free to do it on any difficulty necessary. This guide is for the Rookie playthrough. It doesn't matter which map you do, just that you do one all the way through. Each map has about 5 different parts to it, with weapon stashes in between to stock up on ammunition.
Now, at the start of each section there are 10 enemies. If you can manage to take them out without being caught, then good for you. If you get detected, they add 10 more soldiers. Now, on Rookie, running and gunning is very possible here. I am not sure of the enemy counts on higher difficulties but I'm sure running and gunning will be a lot harder.
And there you go. You can repeat this process for the other maps and get the achievement for that too. If you need a sneaky partner to help you with this, just hit me up and I'll help you out.