I've been sketching new characters for my project, working in my A4 sketchbook. I find this quite intense and so can't seem to do it for very long at a stretch. I find I'm continually breaking off to check emails and Facebook (...OK, that's normal, but this is even worse than normal).
I got a bit grumpy with my first efforts too, but that's the way it is when I start off. Though I've been doing lots of observational drawing recently, sketching from my imagination feels completely different, so I still need to warm up to it.