What are some good techniques for drawing live subjects? I'm not necessarily talking about stand-still subjects either. I'm also talking about the elusive subjects where you need to capture the essence of the pose very quickly.

What are some good techniques for doing both?

Capturing fleeting movement is a skill that comes with time. You train your eye/brain to just use gesture lines to get the shape of the movement, then go back and add details if you have time.

Its very easy to get bogged down with detail and then the position is gone and you're left fiddling with a face or clothing shape. Concentrate on what shape the position holds and use simple lines to get that. People especially in public places often use the same position over and over so you can go back and add in details later.

It does take practice, but the most important part is to remember to initially avoid detail, just go for general shapes and lines that capture the movement or position. All the rest is icing on the cake. And keep sketching - every day, every where.....use television to practice drawing positions, its great fun.