Quick Sketches
I've been carrying my small A6 sketchbook with my in my pocket (now that winter is over, I don't have the luxury of large coat pockets anymore). This is so that I can do quick sketches during my commutes or while I'm waiting.
One thing that kept me from doing this before was that I felt like I needed to find something "worth drawing" before I could sketch. It felt strange just drawing the dirty corner of an underground carriage or whatever building I happened to be waiting in front of. What helped me get over this was realising how valuable these kinds of exercises are to me. I focus mostly on proportions and value and try to get those right as much as possible.