Your scanner will likely save your image as a grayscale.jpg. Many scanners will only allow you to scan up to 300 dpi. If you can scan higher, choose 600 dpi. You have some options now.
If looking for the crispest and cleanest impression, you will need to convert the file to black and white only (no grey pixels). You have two methods depending on what computer software you have available. If you only have Photoshop, you will need to convert your file to one that is in image mode of bitmap. If your image dpi is currently 300 dpi, you can choose Image > Image Size and change your dpi to 600 or higher without changing the inches. Your file will temporarily be quite large but you will then save as a .TIF with LZW compression and this will resize it to something smaller and more manageable. A higher DPI can help with preserving your details and smoother pixelation while bitmapping. For exact steps to Image Mode of Bitmap, see our File Prep Tips.
If you have both Photoshop and Illustrator, you can convert your image to image mode of bitmap as directed above, then place your TIF into Adobe Illustrator, and convert the file to a vector art file via the Live Trace option. This does not always work with all files to give satisfactory results, so with practice, you will learn to recognize which files will give you a vector result you like. After converting to vector, save the file as a PDF or EPS for upload.