Use Gesture Drawing to Quickly
Capture the Energy of your Subject
Gesture drawing's purpose is to quickly capture the subject that you are drawing. The key to gesture drawing is to use speed. Don't let your hand slow down. Let your arm be loose and quick. The goal here is to get an impression of what you are trying to draw. If you let your hand and arm slow down you may be tempted to try and start adding in detail to your drawing. Don't let yourself do this. As soon as you find yourself slowing down a little bit, get your speed back up.
I personally found drawing like this really challenging when I first attempted it. I tend to be really detail oriented, and working so quickly really went against the way I was used to drawing.
If you are also a detail person, don't fight the system! One thing I found that really helped me when I was starting was using charcoal instead of pencil. I find charcoal to be quite a messy medium and it's almost impossible for me to get really fine details with it, so by using charcoal I was able to overcome my instinctive impulse to be overly detail-oriented.
Gesture drawing is a great way to quickly get ideas onto paper, and it's a great warm-up exercise before you start into a more serious drawing. Like any exercise - you should warm up a little bit before you start.
Use this technique to quickly capture the energy and movement in your subject. Don't be afraid to use really long lines because they help carry the momentum of the subject.