Mouths are a great way to show the mood a character you are drawing.
This quick tutorial illustrates how to draw different anime and manga mouth expressions from the front view.
There really is not that much to drawing anime and manga mouths. You can see most things you need to know by simple looking at the examples in this tutorial.
However here are a few defining features of anime mouths that you should remember when drawing:
Anime and manga mouths are highly simplified. The lips are usually not drawn at all and the entire mouth can often be drawn with just one or two lines.
Anime and manga mouths tend to be drawn smaller than normal mouths but depending on a characters expression they can be drawn much larger than normal as well. This is especially true if the character is very emotional (angry or happy).
Drawing Anime and Manga Mouths
Start by drawing the outline of the mouth first. Then fill in the details (usually just tongue and/or teeth).
When shading or colouring the inside of the mouth should be the darkest with the tongue slightly lighter and the teeth the lightest (usually just white).
When drawing the characters head draw the jaw lower for a mouth that is wide open and higher for one that is closed.
Keep these tips in mind when drawing and the rest is simply practice.
You can refer to How to Draw an Anime Girl’s Head and Face for more information on placing the mouth on the head.