A drill we have been known to use called MUF(f) hehe
Movement Under Fire... basically it improves your back players communication with the front players and also helps back players with certain skills like crossing up.
One side has 2 or 3 players spread along the back line with guns. The other side has one back player with a gun and up to 4-5 players without guns. The 1st team may not move from the back line (they can go along the back but not forward) the 2nd team must try to get their gunless players to two key bunkers on what would be roughly the 70-80. The shooter for the 2nd team is there to make sure that the 1st team don't simply hang out and let rip at everything and also to help supress the 2nd team thus allowing the players without guns to move up easily.
The 2nd team's back player can shoot the 1st team and when they are shot they are dead but the 1st team may not shoot at the 2nd team's back player (this can be changed if you want to make if more challenging for the 2nd team's back player).
When one of the 2nd team's gunless players is shot he must return to the back center bunker and start the process again, we normally keep going untill everyone has touched the key bunkers at least once, at which point we will rotate the teams.
It is best to make the players who are "gunless" carry a gun but not live or with a barrel bung/sock so that they get more used to moving with the gun than the relative ease of moving without a gun, the idea is to make it as realistic as possible.
Hope this helps
Mr S.