How to Draw Crowd Scenes. The more comics you draw, the more comfortable you become with drawing your regular cast of characters. Into every comic, however, a crowd scene must fall. Unless your characters are on a deserted island or in some other companion-deprived setting, that is. There are a lot of ways to present the idea of a crowd from the very detailed to the more abstract, but some things are universal no matter how you choose to draw it. Here I will go over those elements.
How to Follow General Guidelines
Map out your scene, focusing on your main characters or action. Even with a crowd around you're still going to want the focus on one or two people, generally speaking. Rough them out, their positions and expressions first, so you don't lose sight of the panel's goal.
Decide how involved the crowd is going to be. If there are onlookers or "extras" who are reacting, make sure to sketch them in next in relation to the focus of the panel or page. From there, the less involved a person in the crowd is, the less detailed they have to be.
Use reference photographs to get an idea of crowd dynamics. Especially note the way people cluster together or space themselves depending on a situation.
Vary the heights and widths of people in the background to make them more realistic. While twins and triplets do happen, unless your scene takes place at a multiples convention, you're more likely to see a variety of shapes and sizes represented in the crowd.
How to Use Time-Saving Techniques
Use representative shapes to show a crowd from a distance or overhead. Think of the classic illustration of a baseball game from high above with the stands filled with colored circles for the fans. While very effective in color, black and white comics can still use this technique depending on the individual style.
Silhouette your figures in the background if your goal is just to give the impression of a crowd or a press of people. Use grays and blacks if the mood of the image is dark or it takes place at night for extra effect. This is my favorite technique, since I work black and white, and really gets the point across.
Copy and paste characters from other pages or scenes to fill in the background if you work digitally. It's a bit of a cheat, yes, but if you created the characters the first time around, then it's only a half-cheat at most. Just make sure they don't detract from the scene or stand out too much, but using them for filler can save you tons of time.