dealing with client over concept

hello to all,

i'd like to know whats your basic questions when a client contacts you for illustrations?
am doin hand drawing fashion illustration and found out that clients mostly dont have any exact idea how it whould look like,what kind of media,size ,kind of papers ,and i quite dont like answer 'up to you',and wish they cold direct me a bit more.
i 'd myself be very picky about lots of thinks i buy
what do you think?