Life Drawing Practice

It had been 5 months since the last time I sketched or did any kind of artwork. So one day after being up for 30 hours+, I decided that I didn't want to waste my day by sleeping but to continue with my drawings. So I decided to draw people once again and this is what I got after 45 minutes. Plus I wanted to go digital versus traditional because I wanted to be environment friendly with paper.

Any thoughts or critiques that I could improve on?