I'd say, draw them reasonably big and then scan them on in a low dpi setting and shrink the image in an image editor.
Note that your aim will be to get a tile of 24 pixels by 24 pixels. That's very small.
Perhaps it might be even better to use your drawings as a template and pixelpaint on top of your drawing once you scanned it in. That's the best way to ensure that you'll get optimal quality.