Starting a drawing can be scary. Drawing on crappy paper (that's a technical term!) can be one way to overcome the fear of the blank page.
When I was first learning to draw, my dad would bring home piles of A3 computer paper from his office for me. It was the large thin folded stuff with perforations down the side. Apparently it sometimes used to spool through the printers and couldn't be re-used - at least that's what he told me!
It was great paper to draw on because there was never any fear of wasting expensive cartridge paper: it was already waste, so it didn't matter if I ruined it. I used to sit in front of the TV drawing actors, newsreaders and the like. Documentaries and interviews were the best because they featured a lot of fairly stationary head shots. For a teenager living out in the country with no access to life classes, it was a surprisingly effective way to practice portraiture and speed drawing.
Drawing the envelopes for The Diary Project was similar - if I messed up an envelope it didn't matter and I felt no guilt about tossing it in the recycling. In fact, I sometimes used to draw on the front and back of a couple of envelopes just to loosen up or to test out new techniques or materials. Now my envelopes are all finished and I want to take what I've learnt into making drawings on 'real' paper with the idea of making a series of drawings that could be sold. Yet even after a year of daily drawing, it's still surprisingly intimidating to sit down in my studio and look at those empty sheets of good paper. Maybe I just need to take a stack of envelopes upstairs to comfort myself with...