[Note: There's censored nudity in this one, so don't click if you're around someone who could be easily offended by black bars.]
In every art student's academic career, there will be the inevitable timed figure drawing activity. Your observational drawing professors will only give you anywhere from 30 seconds to 2 minutes to loosely sketch the general form and motion of the model in front of you. This is both a warm-up activity and for you to get acquainted with a draft of the general composition you'll be working with that day.
In this video, Steve Proko allows himself two minutes to sketch out a variety of forms. I would suggest to pay attention to which details he deems important and how he is able to quick sketch a 'blueprint' of sorts. This takes a lot of practice, of course, but with enough time and effort, you'll be quick sketching with the best of them!