One of the best ways to improve your drawing is to do it every day. The trick is to actually do it. Busy lives get in the way and if you sit down to a large sheet of paper you can talk yourself out of it pretty easy. You may think you just don't have the time to make art.
A trick I learned a few years ago has really helped me to be more consistent in drawing daily. It involves making a calendar. An art calendar.
In my sketchbook I draw out a calendar leaving the boxes open and blank. 
Then every day take my extra fine black pen and draw something in that day's box that represents my day. I then color it with my colored pencils.
An example:
If I forget to do it for the day, or if I just can't think of anything that I want to draw then I usually just put the date. I always try to design each square and experiment with the color palette. 
Some months I put a lot of effort into the heading and artwork around the dates and some months I don't. I always use pen and just go for it. Erasing is not an option. I like that. Some designs turn out great and some not quite, but I learn from every one.
It's a great little exercise and keeps me creating, even on the busiest of days.
