In the following video, I'm going to simplify seven basic human emotions so that anyone can draw them. I'm going to show you how to draw these expressions, as well as how each applies to my character from NINJA! You can also apply this guide to your characters.

There are basically seven human emotions: sadness, anger, happiness, surprise, fear, contempt, and disgustSo, you want to start off with this base of a head with just the eyes and the nose. I made this a very simple head that anybody can draw. It's a circle, two dots, and a little curve for a nose.
If you can start with this very simple base, it will be so easy to draw all the rest. Think of the expressions as graphic symbols. That way you can draw them really easily.
The first emotion is sadness.
Before drawing any emotion, you'll want to draw your base. Then you want to draw these curved lines for the eyebrows. And as you already know, just from making a sad face yourself, basically the eyebrows are curved up. Right? And you also know that a curved mouth with a curve at the top is also part of a sad face, so that's a design feature that you want to memorize. Basically, when you want to make sad faces, you want to have curved lines that bend up.
Let's do anger next.
As you can probably guess, you'll want to use two straight lines that are curved in. That way, it looks like somebody's angry. There are a couple of different variations of this. You can bunch the two eyebrows together, and you can lower them. This is also a shape that you can use for the mouth, in terms of a curve, to make an angry face.
Let's do happy.

This emotion has lots of bendy lines. Happiness is all about curved lines that make the expression seem happy. So, unlike sadness, where it's curved up in the middle, happiness is pretty even. And the more bent or the more curved the curve is, the happier your character looks.

Our fourth emotion is SURPRISE!

Now with surprise, you'll want to use two straight lines. It's really about the placement of the eyebrows. You'll want to place them up higher and find the right mouth shape (see the video for ideas). You can experiment with different shapes.

Let's draw fear.

With fear, it's very similar to surprise, but you actually raise the eyebrows even higher. To show more emotion, you can change the mouth shape.

Our sixth emotion is contempt.

And then with contempt, you'll want to use these straight lines for eyebrows, and you can experiment with asymmetrical eyebrows. That means the left side and the right side might be slightly different. I think with contempt, you're looking for asymmetry, so I also did an asymmetrical mouth shape on this one.

And our final emotion is disgust.

For disgust, I'm also using curved lines. They are actually the opposite of sadness. And so, it's not the same as anger. In terms of anger, I put straight lines. With disgust you're not quite as emotional or as angry. It's sort of an in-between emotion in a way, and so your eyebrows are curved just a little bit. And you can experiment with the kind of mouth shapes that you use.

Apply these emotions when drawing your characters.

So, when you're constructing your characters, you'll want to think of these basic human emotions, and then that'll be your guide to drawing out of your head. Another good tip is to look in the mirror. Analyze your facial expressions, simplify them down, and then apply that to your character.