Over the years I've developed a list of pet peeves in the field of Web design. Some of these things I've done myself in the past; most I've seen on others' sites. They're presented in no particular order. These are not hard and fast rules, and in some cases one or two of them may be appropriate, depending on what you're doing. On the whole, however, these are things to be avoided.

• Dead links & broken graphics. Although I said these rules aren't in any order, this is really my number one pet peeve. If you can't check your links regularly, you ought to take the site off line. There are far too many old, obsolete sites that have been sitting on a server somewhere since 1996, forgotten and full of links to other sites that were abandoned long ago, but are still showing up in the search engines. It shows a lack of respect for other people.
• Non-essential pop-up windows. This one runs a close second in terms of the annoyance factor. It's one thing to use a pop-up window for important content or navigational aids, but when it's just an ad or a cute message, it creates just one more thing that people have to do. There are shareware programs available that will "kill" popups as soon as they appear, and with more and more people using them, you might as well kill the pop-ups yourself.
• Excessive vertical scrolling. The nice thing about a Web "page" is that it can be multiple pages. Making people scroll endlessly by putting all your content on one page is a guarantee that they'll miss a lot of it. Create an "index" page and divide your content into two or more secondary pages.
• Straight-line navigation. When you do divide your site into more than one page, don't make people go from point A to point B to point C. The Web is a non-linear medium, which allows people to enjoy your content in whatever order makes sense to them. Don't try to force everybody to view it the same way.
• No navigation on secondary pages. Make sure that a visitor to your site can always return to the main page from any other page. Preferably you want them to be able to move to any other page. Again, the Web's not a straight-line medium.
• Horizontal scrolling. If you design your pages only for people who use high monitor resolutions, you will alienate the millions of people who still use 640x480 and 800x600. You may not realize it because you're operating at the highest possible resolution, but they're all scrolling back and forth horizontally to see everything on your page. And not enjoying it.
• Multiple frames. Frames may have a purpose to aid navigation, but don't get carried away just because you can. Nobody likes to have to scroll up and down on four tiny little windows to see everything on your site. They'll get frustrated and go away. That's not helpful, particularly if you're in business.
• Annoying animations. Those cute little cats and dogs running back and forth may be attractive at first glance, but after you've had to put up with them endlessly cavorting for ten minutes, your tendency is to hit the road. Animated banner ads may get attention, but too much is just that: too much.
• Large photos and graphics. Huge photos may look nice once they download, but very few people will wait for them to load in the first place, especially on slow connections. Before you add a photo or large graphic to your page, make sure you've sized and cropped them to minimize the bandwidth. Better yet, if you have a photo you think people just have to see, put it on a separate page and use a thumbnail with a link.
• Too many photos and graphics. Too many photos or graphics can have the same effect as large graphics. The cumulative bandwidth drain is the same.
• Reversed colored type on dark backgrounds. Art directors often seem to think that non-white type on black backgrounds has a classy look. That may be true, but it's hard to read. And if people get tired of reading your text, you might as well not have written it. A small block of this sort of reversed text is acceptable, but using that technique for an entire page or even a site is excessive. Stick to white on black or don't reverse at all.
• Busy background graphics. I've seen sites that used such convoluted backgrounds that it almost seemed as if they were trying to discourage people from reading the text. Keep the background simple, clean, and above all, light-colored. If you want to make part of the background dark or complex, restrict it to a band on the left.
• "Under Construction" signs. The Web is always under construction. There's no such thing as a Web site that's finished and will never need to be changed. If your site is really missing something important, don't upload it.
• Streaming audio with no "off" button. You may love that midi version of "My Way," but a lot of people will start looking for the audio controls as soon as they hear it. If they don't find an "off" button, they might hit the "mute" control, but they might also move on without bookmarking your site for future reference because they prefer not to surf with the sound off.
• Disabling of the "back" button. A few sites have come up with code that makes it impossible to leave their site by using the "back" button, unless you click several times in succession or close your browser window. This is dirty pool, and should never be used.
• Generating new browser windows when windows are closed. The porn sites are doing this, or so I hear. They'll eventually crash your browser if you keep trying to close the new windows that open. This is reprehensible, and should not be tolerated. Let's hope this technique is restricted to porn sites only.
• Bad grammar & spelling. If you can't spell, get some help. If you can't write, find somebody who can and ask them to proofread your text. If you insist on eliminating capitalization and punctuation entirely, except for strings of dots, don't expect anybody to take you seriously.
• Crummy scans. Avoid fuzzy photos by learning how to use your scanner and graphics program. Even the cheapest scanner will do a pretty good job if it's properly adjusted. Take a minute and read the instructions.
• Ticker tape status bars. Hijacking my status bar just makes me mad. I like to use it for its intended purpose -- to view download status and to see URLs that my cursor is positioned on. It's not the place for a friendly scrolling message.
• Missing meta tags. Meta tags help search engines to find your site and describe it to people. Without them, nobody will be able to find your carefully designed page. (If you want to see what they look like, click on "View," then "Source" in your browser and take a look at this page's Title, Meta Name=Keywords and Meta Name=Description.)

That's enough preaching for one day! You can probably think of a few more, but those are the no-nos that occur to me at the moment. Violate them at your own risk.