Good suggestions so far.
One thing a lot of drummers overlook is dynamic contrast. Make sure that your ghost notes are as low as possible and your accented notes are quite loud. The ghost notes should sound almost like a hi-hat. If they are coming out kind of "muddy" or if they lack definition, it may be because of your gear. The type of playing that I do typically requires a lot of ghost notes, so my main snare is a
Pearl piccolo that I keep cranked pretty high. If you use a deep snare or a relatively loose head (or both), then your ghost notes won't come out like they're supposed to.
Also...
Listen, listen, listen. Anything with David Garibaldi (primarily Tower of Power), Rick Latham, Clyde Stubblefield (James Brown) and John "Jabo" Starks (also James Brown). If you need some good exercises, check out "Future Sounds" and "The Funky Beat" by: David Garibaldi and "Advanced Funk Studies" by: Rick Latham.