Join up and map out your plan. No matter how simple the plan seems, run it a few times and see how flawlessly it goes. You would be surprised how many times you need to practice the timing on opening a door, covering a window, loading a grenade in time, and throwing it at the right angle before you get it down to a habit. Decide which side each person is on. Your both rushing down the long narrow hallway in the Chalet.
Someone is at the end of it, and starts to shoot.
Don't run down the center, have one guy always be on the right side, and one guy on the left. This prevents inadvertently killing your teammate. It's simple procedures like running down a hallway on the wrong side that can ruin your game. The easiest way to get easy kills is to know where your enemy is coming from. This is fairly easy to figure out if they always do the same thing.