usually I would like to meet them up in advance (and usually more than once meeting) to talk to them.. and for them to know me as well. THey have to be comfortable with you. You can be comfortable as you already know your stuff but they don't and it's important to communicate all that to them.
during the meeting, I dun probe deeply and allow them to be relaxed and you talk about the weather, the latest stuff on the news and gossips (depends on case to case lah,some models dun like to do that or too busy to spare the time) only when you see that they are okie and good to talk business, then you go into it.
during the shoot, as they are professional models or some amateurs, you need to ease them in to the shoot. Start off with chit chatting, occasionally snapping a few casual shots (candids) show them, have a good laugh and then you start directing the kind of poses that will compliment them and meet the requirement of the assignment.
SOmetimes you feel the moment, sometimes you can create the moment by saying something that will expectantly evoke the desired pose of laughter or thinking look. Communication is important... you can't keep quiet and just keep depressing the shutter button.. your models need direction which on ly you can see thru the viewfinder.
I'm still learning the ropes of that and some photogs are simply gifted with their style of putting their models at ease.. example: DIGIPIX aka Jason Ho.. his model shots are really something to learn from.. Wolfgang's model shoot oso has the same effect... Ruthbaby's/ Astin's/ Lorbert's are all good examples where you can pick up in addition to the technical aspects of the shot
if it's for events, get to talk to the people more and snap a candid and then ask them for a group smilie photo.. they are usually obliging