Options - If you have a friend then play co-op, but if you are playing solo then go to a local game and in the options select double health and fast regeneration.
On the map go down into the tunnel and close the door at the far end. Then set up at the bottom of those stairs under the closed door and all enemies will file down right to you. The riot shield guys are a little tricky, but if you save your IEDs they shouldn't be too much trouble. That's pretty much it.