I find that one of the best ways to keep myself on my toes as an artist is to switch up the way I draw things. Since so much of animation, comics, and the like is about finding cool ways to simplify and stylize the figure (or whatever your subject maybe), I like to try new methods in my sketchbook--a great place to experiment and make mistakes.
Also, since I find that I'm not nearly disciplined enough to make changes in my drawing habits on my own, I try to get new materials and tools to draw with to keep me fresh. This latest batch is done with a 3.8 mm nib Pilot Parallel Pen (from my friends at Jetpens.com...that place is a goldmine for cool drawing/writing instruments), which is supposed to be a calligraphy pen, but I thought I'd try it out for this. I'm still drawing in a vintage book that I converted into a sketchbook by gessoing the pages with tinted gesso. This particular book is an old Jehovah's Witnesses tract from the 1960s or 1970s, which makes me smile.
Trees are pretty. I feel like I'm achieving marginal success in ripping off Bill Waterson.
These gestures are done with one of my staples--a Uniball ballpoint (0.5 tip is my favorite).