A quick, messy sketch to illustrate some dynamics in drawing expressions. A lot of you have asked how I pack the emotion into my drawings, and so I figured I might as well do some 'splaining. Basically, every single part of a character is used to insinuate any one emotion. All of them must fall in line before you can really pull it off.

THINGS TO CONSIDER:

-Eyebrows
An obvious part of expression. More stress needs bumpier, thicker brows, while more relaxed or happy emotions requite smooth, thin and relaxed-looking ones. Also note how raised they are from the eyes. The more upset or determined or concerned, or maybe the harder the character is laughing, the lower the brow. As for being happier or more excited, the opposite goes.

-Eyes
Another duh. But the pupil and iris included make the eye equipped with limitless variations of emotion. Adjusting where the eyes are looking is one thing. Happier or relaxed eyes are more focused and are looking in a definite direction. Though sometimes in shock, fear or anger, eyes wander slightly further apart, though not enough to make the character look as though they have a mental disability. Sizes of the pupils, shapes of the eye and how open the eye is are important considerations too.

-Mouth
When in stress, the mouth is stretched and contorted, and sometimes more rough and lined. Relaxed mouths are smaller and less open, to insinuate the mouth is nearer to a non-moving neutral position. Genuinely happy smiles should be wide and show a tiny bit of lip definition, and curl up at the ends, unless you're going for the tiny cute chibi-type mouth. And no matter what the mouth position, don't be afraid to show some teeth. =3

-Facial Lines
The more the face contorts, the more stress lines can be found around the mouth, nose, eyes and eyebrows.

-Shoulders
As shown in the picture, a happy person's shoulders can either be raised in excitement and glee or relaxed serenely and peacefully. Less than happy emotions can cause the shoulders to hunch in fear, anger or deep anguish. Also, not shown in the picture, shoulders can be thrust downward in shock or drooped in sadness.

-Hair
Yes, you heard me. Hair is as expressive as everything else. The hair pretty much follows the same rules as the shoulders. Except you can get even wilder with it...XD

-Hands
Hands aren't supposed to be part of this segment, but the hands should match what the face is doing. Pissed? Clench those digits up until you almost crush 'em. Gleeful? If you're a girl, spread your fingers as if to skip down a yellow brick road! Guys, make fists of determination and manly manliness! Feeling graceful? Have the fingers be doing soft, intricate movements. Or, there is always the neutral relaxed hands-at-your-sides position. But that's Bo-o-o-ring.

This is overall a pretty vague explanation of everything. The key is knowing how to match the intensity of an emotion with how you construct the face. Sometimes even drawing what you feel like at the moment is very good practice too.