Get it all together before you go flag running. You'll need to have it down before expecting to start capping with any efficiency. Once you learn how to move in assault armor, you'll feel like someone unchained you when you're wearing light armor. Chances are you'll become a lot quicker and five times more agile. You're going to need fast feet to cap.
Teamwork is the only viable option against an organized defense.
The quicker you learn that, the better your chances of making a cap. Learning the chat menus will be extremely valuable in coordinating your attacks, asking for assistance, or delivering orders and status updates. A good carpet-bombing or tank run will often be required beforehand to weaken the enemy's defense. Meanwhile, cappers should be waiting for that opportunity. In the meantime, it may even be a good idea to try and further weaken their defenses before going in.