Here are some general tips on posing for the camera. During a photo shoot, the photographer will usually direct the model for any specific poses that the photographer is trying to capture, but it helps if the model knows what to do without a lot of direction.

Some General Posing Tips:

Don't hold your breath for a pose. The concentration usually shows in the picture.
Hold in your stomach to give a more toned appearance to the abdomen (even if you are in great shape).
Most people, including models, do not have very good posture. Unless you're going for a casual look, keep your back straight and your shoulders up.

Don't keep both arms entirely straight unless directed to do so for a specific pose. Bend one or both arms, even if only a little, to make the pose look less artificial. Likewise, don't keep both legs entirely straight.

Don't always look straight at the camera. Instead, use a variety of head and eye positions: Try turning your head, tilting your neck to one side or the other, or looking off to the side for some poses.

Don't use a big smile for every pose. Sometimes try a small smile, a pout, a laugh, a scowl, or even a frown, to give some variety to your facial expressions.

Listen to what the photographer tells you. He can see you through the camera. You can't.
Additional Posing Tips for Plus-Size Models:

Rest most of your weight on one foot or the other instead of evenly on both feet. Doing so makes poses look less artificial and gives a slight slimming effect in most positions.

When sitting or reclining, roll one hip up slightly from the resting surface so that most of your weight is on the back of one thigh or the other instead of evenly on both thighs. This gives a slight slimming effect and makes the pose look less artificial.

Avoid having your arms hanging flat against your sides. Instead, bend your arms slightly, place your hands on your hips, or try other poses that involve alternate placements of the arms.

Keep your chin up to avoid chin wrinkles or double chins.
Posing Tips For Emphasizing Cleavage:

Lean forward.
Bring arms together at the waist.
Clasp hands together below the waist, keeping arms straight at the elbows.
Cross arms.
Posing Tips for Minimizing Cleavage:

Lean backward.
Keep arms apart.
Raise arms above shoulders or above head.