Always, always, always Stick Together

This is the cardinal rule of Left 4 Dead. Never venture away from your team unless there is only one entrance into where you are going, no way for zombies to drop from the roof, and your buddies are guarding said only entrance. Running ahead of your team is a great way to get torn apart by a special infected such as Hunter or Smoker before your teammates can ever reach you. People that just run haphazardly away from their team get strangled, torn apart, and covered in bile. The same happens to those that lag behind for whatever reason, but make sure to stick with your slowest team member. All challenges are easy when confronted by a team of 4 coordinated players.