1. Design Now, SEO Later: First and foremost, don’t wait until after you’ve completed laying out a site to consider SEO. If you are a designer and you aren’t familiar with how design/layout affect search engine optimization, especially post ‘Panda,’ you had better get familiar.
2. Flashing text or images, or risqué animations: At best these things are annoying, at worst they are offensive. They don’t drive conversion. Most people close the window immediately, those that don’t usually have poor click patterns anyway.
3. Spelling or grammar mistakes: These don’t just hurt you with human traffic; they also hurt your search rankings. Noticeable grammar issues are a bad thing, spelling mistakes are unforgivable.
4. Multiple advertisements above the fold: This is another big turn off to both human and crawler traffic. Also avoid advertisements placed inside the content footprint.
5. Music playing on your site: Not even if you’re a musician should you have music automatically start when someone lands on your site. Consider the number of people surfing the internet at work, or anyplace else where sudden noise is unwelcome.
6. Auto-Start Media: The same can be said for any other auto-start media on your site. The immediate attention factor is outweighed by the annoyance factor by at least 2:1, so don’t do it.
7. Unreadable text or fonts: Whether it’s because there's insufficient contrast between text and a background or image, or because a font is too ‘fancy,’ it’s not acceptable for your content to be difficult to decypher.
8. Difficult (or impossible) to read CAPTCHA: Come on, CAPTCHA is used to make sure that people rather than bots are filling out a form… Let me repeat that “FILLING OUT A FORM!” When you have traffic doing the most important thing they're going to do on your site don’t make it frustrating or worse yet impossible to do.
9. Ignore Mobile: Take into account your client’s mobile strategy. At least make the desktop site usable from a smaller device, at best offer your client a true mobile solution.
10. Big blocks of text: Try to keep your copy brief and too the point. Even if you have a long article to display though, it shouldn’t present like a word document. Break up the pages (which will help your SEO) and make sure that reading the page doesn’t feel like crossing the desert.
There are plenty of other No-No's and arguable "Don'ts" in Web Design, and we'll talk about many of them in subsequent posts. But to the above rules, there really shouldn't be any exceptions. So like I said to start this post, if you find yourself doing something on this list, STOP!