How do I choose a drama?

This is often hard. What I usually do:

First, I look at the most watched or the best rated or the suggestions on Asian dramas sites.
Then, I look at the genre and at the synopsis (which is often quite bad and doesn't give you any idea at all but whatever).

At one point, I got obsessed with an actor (maybe you'll guess which one from my drama list ;) ) and started watching dramas because he was in them. That's another technique.