Cheers for the comments guys ! I haven’t updated enough recently but feel I’m starting to get a better feel for what I’m doing. I just spent a week at LARA in Clapham North, London ( http://www.drawpaintsculpt.com/ ) and learnt a huge amount. The tutors are practising artists who have all been classically trained in Florence and the quality of their work is amazing.
They really helped me understand what I was doing and I think I’ll go back for another week in mid August as I have to take annual leave then anyway. Things I worked on were unifying tones, concentrating on shapes instead of features and working on edges instead of lines.
Here’s a long pose I did whilst I was there:

Oh and proportionally I measure up and try to use sight/size rather than rigidly sticking to head measurements.