Apart from knowing what is on the test, it is honestly hard to study for, since it is an aptitude test. It does not measure how smart you are, nor does it completely relate to everything ATC-related. Instead, it asks you questions and runs scenarios similar to what you might need to be able to do on-the-job.
Example 1: If a plane is traveling at 150 knots and is 15 miles away from the airport, how long would it take for the plane to arrive?
Example 2: A plane is descending from 10,000 feet to 8,000 feet and is traveling at 240 knots with a 40 knot headwind. How far will the plane have traveled before it reaches its new altitude?
Then you may see a digitized picture of a cockpit dashboard with all the dials at particular levels, and it may ask, "What is the ground speed of the aircraft?" or "What is the oil pressure level?" These questions just involve being able to read and interpret a static dial image. You could liken it to looking at your car's dashboard and having someone ask you how fast you were going or how much fuel you have left.
Then there is a mini-psychological evaluation that you HAVE to answer honestly. The questions are designed, both in wording and in number, to make sure you answer honestly. For instance, it may ask you if you work well in stressful environments, and then at another point it may ask you if you panic in stressful environments. If your answers conflict, you set off a red flag in the system that you are trying to game it. Be honest.
Don't fret over the test. If you are selected to take the test or just want to feel more informed, buy the "green book" -
http://www.amazon.com/Traffic-Contr...bs_sr_1?ie=UTF8&s=books&qid=1235594975&sr=8-1. The book will also help answer a lot of questions about the job, as well as give you an example of what goes on in training. You may want to get it just as a reference guide to the whole career field, and I'm sure some of the folks here wouldn't mind selling you theirs, (me included!) since we don't really need them anymore at this point.
The whole point of the test is to see how you think. If you do not get a Qualified or Well-Qualified score, it does not classify you as "dumb"; rather, you do not possess the train of thought/pattern of thinking that the FAA believes is necessary to properly assume the role of an Air Traffic Controller.