How/Where to Level Up Staff

[Davy]

I got my staff this morning. I am now Staff Level 4 and don't know where to level it. Once I get to Level 6 (the recharge passive skill) I am fine leveling because I can just use Wither the whole time, but before that, how and where should I level it? I want to level somewhere on either Cuba, Padres, Tortuga, or Port Royal only. I don't feel like sailing somewhere. (Cutthroat Jungle and Isla Tormenta are exceptions).