I paint many commission portraits. My methods vary depending on how much time the client can give me.
If I have as much time as I want- I make regular times with the sitter and paint them entirely from life.
If time is limited, I paint with a combination of sketches, photos and colour studies. Pastels are my choice for the quick sketches because I can get a good sense of colour and light and the composition.
Then I use the references to paint the portrait- usually in oils. I do some pastel portraits as well.
The first layer on the canvas is paint with neutral (usually ultra blue and umber) oils thinned with OMS. I wipe off with a cotton rag, then map out the darks. Then depending on the time I have, I get to blocking in the main areas.
Just a matter of refining from then on. Sounds simple!
Every portrait is a new opportunity to learn. I love to explore a challenging pose and the attempt to get the sense of the person I am painting.

Thank you for such a detailed response! Very helpful!

To me Ala Prima and commissioned portraits don’t go together, usually with a commission there are some preliminary meetings to get to know the client and discover who they are and what they want.
The portrait will usually require multiple sittings, some without the subject if there is a background.

Alla Prima is usually done on a whim with someone you know, main thing then is to get the lighting right, get them to do something that entails returning to the same position, (usually some sort of work) so the portrait doesn’t become stilted.

This is my first post, so Hi from Tipo.

Thanks, i see your point