For a first-time model, standing in front of a battery of lights and an expensive camera can be a pretty nerve-wracking experience, so they will probably be nervous and will find it hard to relax, and this will show in the photos. It's best to start off with some casual seated shots, with low-key lighting and easy poses. Try to get your subject to relax; crack a few jokes, compliment them on their appearance, and generally try to be professional and reassuring. If the subject can see that you're relaxed about it, it will help them to feel at ease too. A glass of wine will probably help too, but don't have too many.
Don't be discouraged if the first few dozen shots don't match up to your expectations. It will take time for the model to get used to the experience, and if you've never tried studio photography before it will obviously take some time for you to figure out the best lighting, pose and camera angle for each shot. It used to be fairly common practice for professional fashion photographers to shoot the first few dozen shots with an empty camera rather than wasting expensive film and processing on a “cold” model.
A good starting pose, and one of the classic staple poses of portrait photography, is to have the model sit backwards astride a dining-room chair with their arms resting on the back of the chair. This position is not only casual and relaxed, it also positions the model's back fairly straight with the head up, and also gives them something to do with their arms. Either position the arms crossed on the back of the chair, or have the model rest their head on their hand.
For portraits photos don't have the model face directly into the camera, because the results will end up looking like a passport photo or a police mugshot. For a starting pose its usually best to have the model turn their shoulders about 45 degrees to the side, turn their head slightly towards the camera, and then move their eyes to look into the camera. As for which side to turn, ask the model which side they think is their best side. Everyone has a best side (or at least they think they do!), so get them to turn that way.
The trick to posing hands is to make them look as small as possible. Position them so that they are edge-on or end on to the camera, or hidden from view. Never pose the model with their hands flat-on to the camera, especially if they are near the face. If the veins in the hands are obtrusively prominent, get the model to held their arms above their head for about 20 seconds.