Look around on the forums, download some tools, and experiment on a practice ROM. A-Map 1.92 and XSE are good starting places- mess around with those and see what you can do. I actually don't do much with Emerald (although it's mostly the same as FR) so I wouldn't be the best at helping you, and even if I did you'd probably be better off trying to figure things out yourself.
If you have any specific questions about how to do something, there's a subforum in the romhacking section here for that sort of thing, which I advise you to use.