Hullo matey
I think I've posted what I know about fishing Negril on the Caribbean forum after a trip in 2003. If you can't find it, it's fairly easy to arrange a charter, and pretty hard to catch fish. A lot of the resorts will pool six of you on a boat, which means an early start, rushing to another two or three hotels to pick up the rest of your party, and $100 each for the privilege of catching nothing with, in my case, a stroppy crew. The inshore waters there, as others have noted, have been absolutely hammered.
If you want a bit of DIY it's not much better. Negril's mostly clear sandy beach but there are some rocky patches and headlands, and you get a few fish around these. I flogged the water with fly and spinner all week and ended up with one small garfish, but I did see four different species of ray while snorkelling, including a shoal of 30lb-plus eagles, and stingrays to 20lb, if you fancy trying a bit of legered bait.
There are a few private boats moored along the beach and I was asked by several of the owners if I wanted to come out for a bit of drop-line (handline) fishing in the evening, but I never tried this in Jamaica. It's fun in Antigua and Tobago when the skippers know where the fish are.
The rest? Great music, people, food, sunsets, beaches, cocktails, beer. Sometimes fishing's not quite so important!