Why do we like some combinations of ingredients, and not others? Are there any general rules?
You have two fairly different questions here: flavor pairing (what combinations taste good), and prediction of flavors.

Prediction

Eat as diversely as possible. Try things with different ingredients and combinations of ingredients. It's best if it's something you've cooked, so you know exactly what goes into it, but even eating in restaurants helps, especially if you look carefully at menus and at what you're eating. Eventually you'll learn your personal preferences better, and develop intuition for what everything tastes like.

There's really no substitute for this in the end, because everyone has different preferences, so ingredients and combinations that taste good to you might not quite line up with what others like. And besides, it's not really possible to describe flavors meaningfully, so even if someone tells you "you'll love strawberry and vanilla together", you ultimately have to just learn the flavors to be able to predict how it'll taste to you.

Pairing

Specifically on combinations, see this previous canonical question. The summary is that again, this can be pretty personal, but insofar as there are common preferences, it's difficult to generalize. Most useful resources end up being long lists of pairings you might like, just slightly more general than looking for recipes that contain one of the ingredients and seeing what else is in them.