I've been studying Loomis (inconsistently) for about a month now, and have just gotten comfortable with drawing the head with graphite. It's still a bit hit and miss, and I'm not exactly sure why - sometimes an eye is slightly out of place, sometimes the nose is a bit lopsided, and so on.
How much longer should I spend on this before moving on to, say, the hands, or the figure? I kind of get the feeling that I'm procrastinating with the repeated head drawings.
If anyone's curious, some head studies can be found in my sketchbook - I'm by no means urging you to look, but perhaps some criticism is necessary.