1. Building your site in flash. Sure, it may look pretty, but the search engines cannot index your website. It’s best to just stay away from this.
2. Images that contain text. If you have something to say, say it with text. When you have an image on your page, the search engines can’t see it. Plus, this the less images you have, the lower your bandwidth rate.
3. Using and abusing keywords. It’s not 1996 anymore; you can’t get high rankings by repeating your keywords 7000 times, and making the font the same color as your background. In fact, this will hurt you in the rankings.
4. Not marketing your website offline. Explain to me again why it’s not on your letterhead, envelopes, business cards, signatures, etc. USE IT EVERYWHERE! Of course, use common sense. A great thing to do is buy 100 moo cards, get them printed up with your best selling content or the star of your site, and drop them frequently.
5. Spending money on marketing that isn’t working. Stop. Just stop right now. No matter how much you think it may work next month, no matter how much the salesman tries to convince you, walk away.