1) Non-descriptive page titles - if you use a WYSIWYG editor, it may be titling your pages the same as the page name. Pages with the same title on the domain will not get listed. The search engines see them as duplicate pages and won't index past the same title twice. Use a short 7-9 word descriptive title for each page and make sure each page title on your site is unique. What do you think is a better title for your page:
a. Home Page -or- b. Blue Solar Lighted Widgets That Play Music
2) No meta tags in page - If you don't put a description meta tag on your page and it gets listed, it will list the first few words of copy on your page. Keyword meta tags are not read anymore by most major search engines and just putting a keyword in a keyword meta tag will not you listed for that keyword.
3) Thinking if you build it, they will come - you watch too many movies... here's your reality check. Submitting your site to the search engines is not enough. Without good optimization efforts, you can't compete for keyword rankings on a global basis.
4) It has to be pretty - that depends largely on the purpose of the site. For the most part, design is subjective. What looks good to one person is unattractive to the next. The search engines don't care what your graphics or animation or color scheme is. It just has to be well organized, well-written, user friendly, consistent, logical to navigate, provide a valuable service and be 'sticky'. Killer sites aren't just aesthetically pleasing, they are highly useful, well planned and easy for the search engines to crawl. The design grabs their attention, the content keeps it.
5) Too much animation - Animation has it's place and can be quite clever and appropriate on a lot of sites if used to the best advantage, but too much of it is unnecessary and will aggravate visitors. Never use blinking text or pop up ads... how do you like them?
6) Cannot resize text - When you build a site you have to take into consideration that the web is not print. It's a movable media that displays differently on each monitor. To be useful, you have to offer options to your visitors. If you use .css, you need to specify the text in .em instead of .pt for the vision impaired and Mac users.
7) Different design for each page or section - How will your visitors know they are still on your site if it's pages are not consistent? You can guarantee consistency by placing navigation in the same place on each page and your logo in the same spot at the top of the page. If you have expandable menu items, put them on every page of your site in the same place. Your visitors will expect it to be there and it's not user centered if they have to learn a new navigation system for each section. Use consistent navigation on every page. A different design and way to navigate it for each section is confusing.
8) Background Music - A different twangy .midi song on each page that loads is the most aggravating thing on the internet. Even an on/off button is aggravating if it has to be used for every page load. Unless it's a presentation that the visitor selects, sound has no place on a professional site and what good does it do to optimize for maximum traffic if you alienate your visitor...
9) Poor maintenance - Orphaned pages are pages in your site that have one way links or no links to other pages. Outdated and poorly written pages with broken links could affect getting your site indexed. A lot of broken internal and external links could keep your site from getting indexed.
10) Main focus - You can have several topics on your site, and indeed you should have for interest and support. But there should only be one main focus that tells what your site is all about. One main subject that lets your visitor know exactly what most of your content is. What is the purpose of your site? Spell it out with your headlines, tag line and graphics. If it's not apparent by looking at the main page, your visitors have no reason to dig deeper.
There are a lot more mistakes site builders can make, some biggies and some minor, but correcting the ones listed here will make the biggest impact on your site as a whole and the ability to get it listed properly, and they're so easy to correct.
