the less light the better
what triggers do you have?
i'm guessing they wont have TTL.. which will limit your shutterspeed to like 1/200th ish.
are you familiar with
www.strobist.com ? (shooting manual flash and manual mode on the camera?)
you will want to make sure your stand doesnt blow over (assistant or sandbag)
make sure the flash is exposing the person a stop or two (to taste) brighter than the background
kinda hard to give specifics without a specific question i guess.. i hope this helps anyway.