You often hear such sayings as “listen to your gut feeling” or “decide intuitively”, which of course makes sense, since no one can tell you which subjects to choose, but they don’t make the selection any easier. You can’t know how you like a subject until you’ve actually had it.
Choosing an IB subject should be a subtle combination of what piques your interest, but also challenges you in the right way. An ideal subject would be one that you have some level of knowledge about and would like to learn more about. It should also be challenging enough that you have to work for it, but not overwhelm you.