Depends on where I'm going, whether I've been there before, and how long my trip is, but as a rule I'll always seek out the local food and try to see a mix of famous big-name sights and weird niche things that interest me. For example, when I was in Tokyo last, I went to the top of Tokyo Tower at sunset (normal tourist sightseeing thing) and also went to see their underground flood-control tunnels.

I don't enjoy "sit on a beach and do nothing" vacations, but more power to you if that's your style.