This is the biggest secret of the advanced player and the biggest mistake that a new player makes. It takes a while to learn and use, but is a great investment. Immediately after the starting horn sounds, players will run to the first piece of cover and hide behind it.
Inexperienced players jump right up and hide directly behind the cover.
They are way to close. Being this close limits your sight. This will hurt you. You have to be able to see what is going on. You have to maintain eye contact with the field of play at all times, hiding this close takes away your ability to maintain eyesight with the entire field.