Just got back to drawing. Would like some pointers.

Just got back to drawing after a long time because I finally got a tablet for digital drawing and it's clear i am lacking certain skills, so I thought that it would be move effective to ask other people where to start improving and get some critisism.

Here is the first "finished" drawing i've made in about a year and a little more.

I welcome all kind of advice, even harsh ones ! Thank you !