Don't always plan a defensive game unless you're starting area has great defensive terrain. Most of the teams I ever see win are aggressive teams. I don't me be crazy or go on a suicide mission. The only way you can win is with very good communication skills. You always have to tell your fellow teammates were you are, what you're doing, and whom you killed.
Communication is very important and a skill that is hard to develop.
Infiltration can be devastating to an opposing team. To do this you usually have to go up the left or right side of the field. You have to be very quiet and you have to move very quickly. Only the best teams can master this technique. Remember when you go up one of the sides of the field don't bring your whole team bring two people who are fast, quiet, and have good aim.