It will take a while to contribute much with *any* class, because the number and nature of things you have to pay attention to is greater.
Learn the maps. Playing in the lowbie bracket gives you a good chance to understand the basic objectives, the terrain, and some basic strategies without people raging at you for stinking. You probably won't see more than rudimentary strategy, because coordination in this bracket is usually nonexistent. Learn to keep an eye on your minimap. Even if you are pretty bad in the actual fighting, being in the right place at the right time can help your team greatly (and is something that will only get more valuable as you become better).
Eventually you have to learn the wrinkles of your class and everyone else's class, but understanding the objectives is foundational.