Chris, I try to read up every time I go to another country. It serves two purposes. One, I enjoy the trip more, two, I don't offend anyone.
Local customs are different everywhere. In Dominican, for instance, EVERYONE tips each other for everything. That's the locals, tourists, literally everyone. You tip someone if you just ask them for directions or information about what's in a shop. You have to have a never-ending supply of dollar bills.
That said, Frommer's makes great guides.
I just found their guide to Esteli online.
There's not much there, but there's also a forum. Hit wikipedia and stuff like that. You'll be glad you did.