How to level up quick

[Zhalin]

If you're under level 20, at Fort Charles. Just work your way through time after time.
Also, some people have already figured this out, but...on top of the gallows is a Grunt. A bugged Grunt. Who won't attack you (I don't think) while he's up there. Once he's on the ground, he'll attack you, but if he follows you back up the stairs, he'll just stop. And the grunts are from level 14-18, so...it's a nice start.
As for level 20+, I can't pick out just one way. I'm only around level 22. But the story quests around that level (for most) are usually repetitive, and award you a lot of 100 point notoriety boosts. So I'd say keep up with that. Or just go into the Navy forts, like Kingshead. But be stocked on tonics, of course.
Sorry I can't help more.