I've heard that the tests are a lot like AP tests if you're taking AP classes, so try to take similar ones to your AP's. be careful, though because then schools might think you're taking the easy road out

One more important thing to keep in mind is that colleges will either ask for specific SAT II tests or they will want a well rounded student. This means that if you're unsure what SAT IIs to take, try to distribute them across subject areas. If you're a strong English student, pick a math or science subject that you are good at and take that test.

Don't worry if you don't get a perfect score. A student with great writing and english scores + a good math score looks a lot better than a student with great writing, english, and literature scores.

One thing that might help you out here is to consider what high school courses you have taken. Most subject tests test basic information in subjects you probably have already taken in high school. If you thought that you were a strong biology student, then you may want to take a subject test in that area. Furthermore, keep in mind that the Collegeboard writes both SATII tests as well as AP tests, and many of these will be similar. In other words, if you are taking an AP Bio class and are preparing for the AP test, i would recommend taking the SATII test as well. Finally, dont wait till the last second to take subject tests -- taking them right as you come out of the relevant courses means that the material is fresh in your mind, and you will have to study less for them.