People - think of blocks, postures and shapes not line.

Forget the details, focus on the simple shapes.

When you are sketching people in a scene they may not stay there for long so you have to be quick.

So concentrate of getting the basic shape of the body, the angles and the direction, and look at them in blocks of colour or light and shade.Start with 'stick men' if it helps, but try different ways of attacking the subject and it will get easier.