This is obviously a level specific achievement and can't be missed (unless, of course, you don't finish the mission).
This isn't a step by step, but a few pointers to get through this mission much easier.
- Do not use this mission as the mission to go completely hidden on (I did, and was so much easier not doing this) - there are lots of clusters of enemies to take down. If you choose this route, save early and often, you'll need it.
- Before the final general at the end of the level, place 3 landmines within the tire tracks in advance. Once you kill the final general, you will only have a limited time to set this up.
- If you don't have the above mentioned landmines, there are 2 of them in the last area where you kill the general.
- When you kill someone, try to dispose of the body. They will find them, and ultimately you if you are not on the move.