I once took some body language classes in a previous job to help me learn both how to read people and how to present myself. One of the tips that stuck with me from it was that when you lean towards a person that you’re interacting with you present yourself as interested and engaging. Similarly – if someone else is leaning towards you they are probably listening to you and are engaging with what you’re saying.
A similar thing can be conveyed in portrait photography.
When taking an upper body portrait a simple way to make your subject more engaging and friendly is to have them lean in towards your camera a little.
You don’t need them to lean in or bend over too far – but even having them do it just a small bit can help. Another way to give the impression of your subject leaning in is to photograph them from slightly above (as in the image on this post).
Alternatively if you are wanting a more formal portrait you’ll probably want to post your subject in a more upright position with them sitting up straight.
Lastly, if you’re feeling like experimenting with leaning your subject back away from the camera it’s possible to create a feeling of joviality as if they are leaning back for a belly laugh. Of course leaning back can also make your subject look quite uncomfortable and even defensive and it’s a pose that I tend to avoid.
Get more posing tips at What Everyone Should Know about Posing for Portraits.