Create a character. Make sure that the character---it could be a man, a woman, or a gigantic sea cucumber---has qualities that people can identify with. Write down the character's physical and mental attributes before you start drawing a comic strip. This will help you keep the character consistent over time. Does Dilbert ever change? Online comic strip characters don't change either.
Map out a storyline if you want the comic to be either lengthy or a "to be continued" type of strip. Keep it short, as the attention span of people surfing the web is notoriously short. Use a "one-liner" style for short comic, as in "The Far Side."
Draw your comic. Stick to simple lines and backgrounds for the greatest visual effect. Use fine-tipped black markers to outline your work so that it will scan well. Color is optional. Use Paint or another illustration program if you are so inclined. Using web-friendly colors to begin with will ensure that your work will really "pop," if you are creating comics in color.
Scan your comic---if you have not created it in an illustrator program. Hewlett Packard recommends that you "choose a lower ppi (scanning resolution of 75 or 100 ppi) for images that you'll send via e-mail or post online." This decreases the file size, an important consideration when putting images online. Web surfers generally will not wait for a large file to load, and will move on to the next website.
Save your comic as a GIF, as this will result in a smaller file size than saving it as a TIFF or other file type. Again, loading time is decreased when you choose a small file size.
Upload your comic strip, known as a "webcomic," to your website. Purchase a domain especially for your web comic if you are serious about attracting a following. Having your own domain will make it easier for people who like your comic to return to your site.