For super easy kills on the fuel plant map, just get up on to the balcony overlooking everything and shoot the opposition, also from near where the trains are, there's a re-spawn point then there will be a crate of oil tanks, crouch or phrone on the right side of the barrels and pick everyone coming down the central column

Another tip for both modes is when you have a long range gun: KAR 98K, Lee enfield. FG42 etc use it to your advantage by going for people that cant see you or are on the pause menu.

Also on the fuel plant map there are some stacked barrels there are little spaces in between shoot through their because for the opponent to get you they've got to be good at the game to aim 100 yard through a small hole that the bullet will only just fit through.