It's very important not to get caught with your head down in a bunker, especially if you're being fired upon heavily. This usually means that someone is making a move on you. If someone is shooting steadily at you, let your teammates know. Chances are someone can shoot the guy that's bothering you. Those five words let your buddies know that you're being shot at and where your being shot from.
Many fields have tall grass that makes for perfect crawling.
When you're crawling close to you opponents, wait until you hear his gun firing to move. This will mask any noise you will make. When you are looking at a field before the game starts, try to find spots that are below your opponents line of vision. Many times you'll find that you can crawl out in the open without the bad guys knowing. This can really surprise the other team.