My favorite warming up activity before starting any illustration assignments is loosening up with some blind contour drawing while listening to audiobooks or podcasts. This is one of my favorite creative exercises, a takeaway from The Natural Way to Draw by Nicolaides I read years ago. I find the constant practice of making the hand and the eye work harmoniously very similar to meditation: sometimes it’s hard to stay afloat, but sometimes you really get to ride that wave. As long as you stay with it.
p.s. Yuko Shimizu addresses the similar approach (along with some other very valuable ways to practice drawing) in her Skillshare class Learning How to Draw: A Mindset, Method, and Exercises which I highly recommend if you’re in a creative rut or if you (like me) have little kids and need to reset the mind from the chaotic parenting routine and start the work day fresh.