Instructions
Select the Mii Channel from the main Wii Channel menu on your remote. You will see the "New Mii" icon, which is a green smiley face next to a speech bubble with a "plus" sign inside. Hover over the icon with your remote and push the "A" button to select it.
Choose whether you would like your new Mii to be male or female. You can then select "Choose a look-alike" and pick from a selection of pre-made Miis, or select "Start from scratch" to create one of your own.
Experiment with hairstyles, hair and skin colors, facial features, face shapes and clothing until you like the way your Mii looks. You can try to make your Mii look like you, a friend or even a celebrity. There are several websites, such as Mii Characters (see Resources), that give detailed instructions on how to make Miis that look like celebrities and cartoon characters.
Select "Quit" if you don't wish to save your new Mii, or "Save and Quit" if you do. If you save the Mii, you will be prompted to choose a nickname for it. This can be your name if the Mii is meant to represent you, or any other name.
Repeat this process to make another new Mii. Your Wii console can store up to 100 Miis at a time in the Mii Plaza, and your Wii remote can store an additional ten.