Representing a moving crowd – if figures are vertical they look static, if figures are slightly diagonal they look at if they are strolling or walking along, if figures are nearer the horizontal they look like they are moving faster. That is the easier way to remember how to make a figure of a person look like it is moving. Another way is to show the sole of a shoe, from walking towards or away from.
If there is a particularly tall person in a crowd, in relation to the rest of the crowd, it is advisable to make that person nearer the height of the rest of the crowd unless of course you really want that person to stand out as the focal point.
Figures should cross the horizon line otherwise the perspective is incorrect. Two ways to simplify figures: the carrot or the stick. It is very easy to draw a carrot shape, and then a circle above, and then use that basic shape to make the shape of a person, their clothing, any item they are carrying and also their cast shadow.
A crowd of people walking along in a painting can create a fantastic sense of the design principle of movement. Spend time on each figure to give it personality and identity. In the crowd in the scene I have painted you can see a wide variety of dress, items carried, colour of heads of hair, just a few elements that give each figure its own identity.