When moving through open ground with no cover, have someone on your team give you cover fire. Move quickly, and never stop in the open. Try to run a zigzag pattern. Scan ahead for suitable cover that will hide your whole body. When you get good cover, look around, and when you are prepared to give cover fire, have your teammates advance in leap-frog fashion.
Rookies usually stay in one place too long.
If you stay put too long, the other team will find you and shoot you. Do not let your fear of being shot for the first time make you play too cautiously. If you have a fear of being shot, you need to force yourself to be aggressive. Usually after the first couple of times the fear of getting hit leaves you. Another good habit to develop is to check behind your back every so often.