Here are a few ones from this summer, and the process for each one was different.
Ursula is very talkative with a great big mouth full of teeth: this is where I started (and I forgot her glasses).
For Fabien I drew first his gentle eyes. (He would like to look like a bad guy, but he has definitely a friendly face)
For Cat Gout, I started with the glasses sliding down on her nose (she looked a little surprised at that time).
And Pete had this very concentrated attitude while he was drawing a portrait of Gerard Michel in Barcelona, I did not have to move from my chair to draw him, and I think he did not even notice me.