@drawerduck

Using pen is a great way to spot errors and resist the urge to over-erase. But if it starts feeling like a chore, I'd stick with whatever you're drawing most, since keeping up the volume matters more than the tool. Construction lines are a superb tool for practice, and a sketchbook is a practice book, so use them whenever they help. I'd also treat your sketchbook as a work book: don't hesitate to circle your mistakes and write them down so you can review them again a few days later. Keep the amazing work with the 30 day challenge !