There are several lists of web design mistakes around the Internet.
Some of the points are common sense, others are quite polemic. Most of them apply to any website though, whether we talk about a business entity or a blog. Enjoy!
1. The user must know what the site is about in seconds: attention is one the most valuable currencies on the Internet. If a visitor can not figure what your site is about in a couple of seconds, he will probably just go somewhere else. Your site must communicate why I should spend my time there, and FAST!
2. Make the content scannable: this is the Internet, not a book, so forget large blocks of text. Probably I will be visiting your site while I work on other stuff so make sure that I can scan through the entire content. Bullet points, headers, subheaders, lists. Anything that will help the reader filter what he is looking for.
3. Do not use fancy fonts that are unreadable: sure there are some fonts that will give a sophisticated look to your website. But are they readable? If your main objective is to deliver a message and get the visitors reading your stuff, then you should make the process comfortable for them.
4. Do not use tiny fonts: the previous point applies here, you want to make sure that readers are comfortable reading your content. My Firefox does have a zooming feature, but if I need to use on your website it will probably be the last time I visit it.
5. Do not open new browser windows: I used to do that on my first websites. The logic was simple, if I open new browser windows for external links the user will never leave my site. WRONG! Let the user control where he wants the links to open. There is a reason why browsers have a huge “Back” button. Do not worry about sending the visitor to another website, he will get back if he wants to (even porn sites are starting to get conscious regarding this point lately…).
6. Do not resize the user’s browser windows: the user should be in control of his browser. If you resize it you will risk to mess things up on his side, and what is worse you might lose your credibility in front of him.
7. Do not require a registration unless it is necessary: lets put this straight, when I browse around the Internet I want to get information, not the other way around. Do not force me to register up and leave my email address and other details unless it is absolutely necessary (i.e. unless what you offer is so good that I will bear with the registration). (great alternative is the use of open source id).
8. Never subscribe the visitor for something without his consent: do not automatically subscribe a visitor to newsletters when he registers up on your site. Sending unsolicited emails around is not the best way to make friends.
9. Do not overuse Flash: apart from increasing the load time of your website, excessive usage of Flash might also annoy the visitors. Use it only if you must offer features that are not supported by static pages.
10. Do not play music: on the early years of the Internet web developers always tried to successfully integrate music into websites. Guess what, they failed miserably. Do not use music, period.
11. If you MUST play an audio file let the user start it: some situations might require an audio file. You might need to deliver a speech to the user or your guided tour might have an audio component. That is fine. Just make sure that the user is in control, let him push the “Play” button as opposed to jamming the music on his face right after he enters the website.
12. Do not clutter your website with badges: first of all, badges of networks and communities make a site look very unprofessional. Even if we are talking about awards and recognition badges you should place them on the “About Us” page.
13. Do not use a homepage that just launches the “real” website: the smaller the number of steps required for the user to access your content, the better.
14. Make sure to include contact details: there is nothing worse than a website that has no contact details. This is not bad only for the visitors, but also for yourself. You might lose important feedback along the way.
16. Do not use blinking text: unless your visitors are coming straight from 1996, that is.
17. Avoid complex URL structures: a simple, keyword-based URL structure will not only improve your search engine rankings, but it will also make it easier for the reader to identify the content of your pages before visiting them.
18. Use CSS over HTML tables: HTML tables were used to create page layouts. With the advent of CSS, however, there is no reason to stick to them. CSS is faster, more reliable and it offers many more features.
19. Make sure users can search the whole website: there is a reason why search engines revolutionized the Internet. You probably guessed it, because they make it very easy to find the information we are looking for. Do not neglect this on your site.
20. Use text navigation: text navigation is not only faster but it is also more reliable. Some users, for instance, browse the Internet with images turned off.