Start the second level on the second chapter.

Go to the point where you have to try and get Neville out.

Hold your squad when you go down the ropes. Make sure you bring C4.

Go up to the window and throw the C4 in, if you want CQB XP you should take out the guard in the back.

Then hide around the corner use the satnav to see when Neville dies, then blow it up.

Then go to reload checkpoint and you go back to the point when you slide down the ropes - do it again and again to get more XP!