Trying to decide which SAT Subject Tests to take?
The best place to start is by looking at your current course schedule. If you are in any AP or IB classes right now that correspond with an SAT Subject Test, there is a good chance that the curriculum for the course will overlap with the test content. Since you are already studying for that AP or IB exam, the Subject Test should require minimal prep work.
If your school does not offer AP or IB courses, or if you are taking an honors or advanced level course that you think would be good preparation for a Subject Test, ask your teacher about it. S/he should be familiar with the Subject Test content and be able to tell you if the course you are currently taking will prepare you.
Once you have decided on some options, take a practice exam in each subject. Your performance on the practice exams should give you a sense of which tests you will do better in.
Remember, as long as you are registered for at least one, you can change your mind about which Subject Tests you’re taking (and how many) up until the day of the test!