Source: How to Dotcom by Robert McGarvey
This could probably be called the top 100 mistakes--there are just so many goofs site builders make--but let's narrow the focus to the most disastrous 10. Avoid only these gaffes, and your site will be far better than much of the competition.
1. Not planning your site.
Before you begin building your Web site, sit down and define your purposes and goals for your site. Then, map out the flow of your site, starting with your home page through every page that follows, based on your goals. Your site's purpose--whether it's to gather leads for your service business or to sell your homemade confections--should drive the design of the pages and the site. If you start building without a firm idea of what the end product should do and be, it'll be very apparent to your users who'll see a hodgepodge of links and information without a unified message.
2. Failing to put contact information in a plainly seen location.
If you're selling, you have to offer visitors multiple ways to connect to you. The smartest route is to put a "Contact Us" button that leads to complete info--phone number, fax number, mailing address. Even if nobody ever calls you, the very presence of this information will comfort some visitors. Always put an e-mail address at the bottom of every page
3. Broken links.
Bad links -- hyperlinks that do nothing when clicked--are the bane of any surfer. Test your site--and do it weekly, to ensure that all links work as promised.
4. Outdated information.
Again, there's no excuse but it's stunning how many site builders lazily leave up pages that long ago ceased to be accurate. When information changes, update the appropriate pages immediately--and this means every bit of information, every fact, even tiny ones. As a small business, you cannot afford the loss of credibility that can come from having even a single factual goof.
5. Too many font styles and colors.
Pages ought to present a unified, consistent look, but novice site builders--entranced by having hundreds of fonts at their fingertips plus dozens of colors frequently turn their pages into a garish mishmash. Use two, maybe three fonts and colors per page, maximum. The idea is to reassure viewers of your solidarity and stability, not to convince them you are wildly artistic.
6. Orphan pages.
Memorize this: Every page in your site needs a readily seen link back to the start page. Why? Sometimes users will forward a URL to friends, who may visit and may want more information. But if the page they get is a dead-end, forget it. Always put a link to "Home" on every page, and that quickly solves this problem.
7. Disabling the back button.
Evil site authors long ago figured out how to break a browser's back button so that when a user pushes it, several undesirable things happen: There's an immediate redirect to an unwanted location, the browser stays put because the back button has been deactivated, or a new window pops up and takes over the screen. Porno site authors are masters of this--their code is often so malicious that frequently the only way to break the cycle is to restart the computer--but this trick has gained currency with other kinds of site builders. My advice: Never do it. All that's accomplished is viewers get annoyed.
8. Opening new windows.
Once upon a time, using multiple new frames to display content as a user clicked through a site was cool--a new, new thing in Web design. Now it only annoys viewers because it ties up system resources, slows computer response and generally complicates a surfer's experience. Sure, it's easy to use this tool. But don't.
9. Slow loading times.
For personal and hobby sites, slow server times are the norm, and since much of this Web space is free, there's really no complaining. But slow server and page loading times are inexcusable with professional sites. It's an invitation to the visitor to click away. If your server is the culprit, find another host. If your Web pages are to blame, make sure you haven't packed them with too many images and applets.
10. Using leading-edge technology.
Isn't that what the Web's all about? Nope, not when you are guaranteed to lose most of your viewers whenever your site requires a download of new software to be properly viewed. Flash is way cool, no question about it, but if nobody actually looks at them, they are just so much waste. Never use bells and whistles that force viewers to go to a third-party site to download a viewing program. Your pages need to be readable with a standard, plain-Jane browser, preferably last year's or earlier. State-of-the-art is cool for tech wizards but death for entrepreneurs.