If you have a closed practice, have a coach stand at the back and help prod people verbally. Say things like "What bunkers are hot" "What's the count" "Who's on bag 1?" You don't even need guns or paint to do these drills. Also if people aren't listening, coach can shoot people in the rear to help motivate
Getting into the habit of communicating, answering those questions, will go a long way in improving overall communication.
Normally a back center player helps relay the calls from each side of the field. Basically acting as a repeater, and also he/she can see the majority of the field and will initiate most calls.
So as a back player, I'd call 2 d-side, or 3 snake on break out, by looking at how many guys are aiming each direction. On the break I'd be yelling (in example above) Orange, bag 1 hot. Kill 1 orange, (teammate) look inside, or wrap on bag1.
I'd probably hear things like, "back left, and snake 1", So I'd yell out "back left, back left, snake 1 snake 1 snake 1"
Normally I'd repeat kill counts and major bunker moves 3 times so people can process what I'm saying.
Also try and pitch your voice lower, it's easier to understand.
I've heard some players get excited and climb like 4 octaves when they yell and it's just like listening to a kettle scream. You can't understand a thing.