I was asked by a sound company that was new to the whole DJ thing about how to set up sound for them. The gave me a list of stuff they had thought of and well...it was very wrong. I thought you guys may enjoy knowing about this as you may some day run into this situation.
There's 2 kind of DJs in general, there's the prom party DJ and then there's the big DJs. Not to undermine the prom DJs, just that they offer far less complications.
The first kind will usually come with a rack with his CD & MD Players, throw ya a stereo out and may (may!) require a monitor mix.
The second...well, thats fun! You very probably have to provide all equipment, and they may (and very probably will) have a rider, I know I have. I only go to play with my LP cases and Headphones. Most DJs will as for 2 turntables, prefered by most (not to say all) are the Technics SL1200 MKII or SL1210. Anything above that is great too. They will also ask for 2 CD players. As something to mention, Denons are usually OK, as long as they're in the 1800F - 2600 models. Nevertheless with the advent of digital turntables, most may ask for these (Pioneer CDJ-1000, Technics SL-DZ1200 to name the 2 big ones right now). They may also ask for a certain brand of mixers (its Allen & Heath XOne for me). You may then start getting extras, like more turntables (I use 3) or an FX Unit (I use the Pioneer EFX-500 but I won't die if they can't get it).
Monitors are a BIG deal as well, there's some seriously deaf guys mixing there. Personally I just use them in the mix but have them off or low the rest of the time, some guys crank it up and leave it there!!! Monitors can range from a pair of simple wedges slightly elevated (closer to the head), to have subs, to a whole system, I just did a gig with 2 KF850+SB850 per side for monitors....ouch!!!
Gotta take care now with excessive vibrations (building booths is a whole artform in itself to avoid this) so you won't get rumble on the tone arms, or worse, have the stylus skip.
As an end note, when setting levels, have the mixer peak at the LED before last. I can stick to 0dBu...most will go all the way.
Hope that helps someone some day, and please don't doubt to ask if u have doubts!!