It kind of all depends on what you're wanting to do with the charm and what materials you have at your disposal. The simplest charm I can think of would be if you created a sigil for your intent, drew it out on a piece of paper, charged that, and carried it with you.
You could go fancier and try making a clay representation to carry or put on your work space.
If you're doing a protection thing and have some string or rope and bells and/or beads you could make a witches' ladder.
It's really up to you where you want to go with it.