these are just some suggestions for a better chance of survival in the OAs
Junk Yard: one person on each side then a safety back a bit farther, or two people back one person kills as much as he can in the front line
Main Gate: because some melee weapons have limited range, they cannot hit the corners of the sandbags so others with guns should guard those points
Rooftops: One person attracts zombies at the very top of the map and shoots and injures as much as he can, the others stay a bit back and get the remaining
don't judge me so much on this, these are just some hopefully helpful suggestions
hope these help! add some other suggestions too