Since I got a mail from a professional, which said I should do more of those drawings as well, I'll give you what he said I should draw, so maybe you can get some ideas as well:
- Draw your own room (Make a mess of your room for extra challenge! ) - Make quick sketches (taking around 5-10 mins)of people in a town or at home - Redraw some landscapes - Redraw vehicles and/or objects
If you want to do more digital painting: - Paint an apple, peach, banana,.... - a self-portrait from a picture of yourself or from a mirror - Paint a landscape from a picture
I'm going to try them all, I hope this will help you as well!