A Candid Portrait Sketch

I have begun sketching portraits to start my studies in this field. As I've been wanting to do this for some time now and have been reading and watching others painting but have to date done only a handful of paintings myself.

I have also recently heard that my proposal of a portrait project that I schemed up last year has been approved for a 3 month residency program at my local arts centre.
This will give me the time and my commitment to develop my skills in this area.
I find now that I need to start at the basics and going right back to learning to draw.
Today was my attempt at looking at the planes of this three quarter candid shot. I haven't yet gotten this far in my studies so I'll go back now and study this before I go further with this piece.
The photo was taken on my iPhone when I was having coffee with my friend. I needed help figuring out how to stop my phone from making too much noise as I tried to sneak a few shots. I would like to sit and sketch there also but people tend to notice the sketching but not if they are also on their own gadgets and mostly they are in the coffee shops these days. This woman was chatting with a friend and that was a whole other problem of catching a good shot with a moving model. I suppose I could have taken a video also and it would have been quieter.