Study poses of people in portraits you like, and try to copy those poses.
Check poses in modeling publications. While you are studying the poses you
might also consider studying the lighting.

Realistic looking dolls are available at your local "adult" gift store. An
air compressor is helpful. Also a patch kit.

Artistic posing is an artistic skill. You don't pose a person so that they
are structural. You pose them so that they look good. In fact, if they are
structural, the pose probably won't look good- there's an old rule in
posing: "If it's comfortable, it's wrong"