People choose keywords that in their mind are descriptive of their website but the average users just may not search them. The keywords must represent how the user approaches the site. Stick with the common lexicon and away from jargon.
All FLASH
Flash might be attractive but not to search engines and users. If you really insist that your site is Flash-based and you want search engines to love it, provide an html version.
Lack of Consistency
If you want to be successful in this competitive market, you need to constantly analyze and maintaing your site, keep an eye on the competition and changes in the ranking algorithms of search engines.
Images vs. Text
Many people think that an image looks better than text for headings and menus. Yes, an image can make your site look more distinctive but in terms of SEO images for headings and menus are a big mistake.
Domain Name
Having a keyword as part of URL is a big bonus when attracting search engines. Yes, it is possible to rank high even without keywords in the URL but all being equal, if you have keywords in the URL this gives you additional advantage over your competitors.
Backlink Spamming
It is a common delusion that it more back links are ALWAYS better and because of this web masters resort to link farms, forum/newsgroup spam etc., which ultimately could lead to getting their site banned.
Wrong Keywords 
