When a character can’t find cover, the next best thing when bullets are flying is to drop flat to the ground.
Ranged attacks against him suffer a –2 die penalty. A standing attacker using Brawl or Weaponry to attack instead gains a +2 die bonus.
A character can drop prone at any point before his action. Dropping to the ground costs his action for the turn. Getting up from being prone also takes your character’s action.