Get yellow, orange, pink and green highlighters and tell your guests to bring white shirts or you can provide them. You also need highlighter bottles, detergents and decorations. You also need good music or a good enough DJ. Check out www.ehow.com/way_5312287_black-light-party-ideas.html for more tips.
Just the concept sounds fun lol. I know that at one party went to like that, people broke glow sticks into the punch so it would glow and no one got sick or anything. Lol weird right? Umm maybe get some strobe lights and fog machines or something, and some loud dubstep/dance music. And alcohol :)