1-Targeting the wrong keywords:
This is a mistake lots of people make & what is worse even experienced SEO specialists make it. People select keywords that in their mind are descriptive of their net site but the average users may not search them. For example, in case you have a relationship site, you might discover that relationship guide does not work for you, although it's the relationship keyword, while dating advice works like a charm. Choosing the right keywords can make or break your SEO campaign. Even in case you are resourceful, you cannot think by yourself of all the great keywords but a nice keyword suggestion device, for example, the Net site Keyword Suggestion device will help you find keywords that are nice for your site.
2-Ignoring the Title Tag:
Leaving the <title> tag empty is also very common. This is one of the most important places to have a keyword, because not only does it help you in optimization but the text in your <title> tag shows in the search results as your page title.
3-A Flash website without a html alternative:
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. Here are some more tips for optimizing Flash sites. Search engines don't like Flash sites for a reason a spider can't read Flash content and therefore can't index it.
4-JavaScript Menus:
Using JavaScript for navigation is not bad as long as you understand that search engines do not read JavaScript and build your web pages accordingly. So if you have JavaScript menus you can't do without, you should consider build a sitemap (or putting the links in a noscript tag) so that all your links will be crawl able.
5-Lack of consistency and maintenance:
If you want to be successful, you need to permanently optimize your site, keep an eye on the competition and – changes in the ranking algorithms of search engines.
6-Concentrating too much on meta tags:
A lot of people seem to think SEO is about getting your meta keywords and description correct! In fact, meta tags are becoming (if not already) a thing of the past. You can create your meta keywords and descriptions but don't except to rank well only because of this.
7-Using only Images for Headings:
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 because h2, h2, etc. tags and menu links are important SEO items. If you are afraid that your h1 h2, etc.
8-Ignoring URLs:
Many people underestimate how important a good URL is. Dynamic page names are still very frequent and no keywords in the URL is more a rule than an exception. Yes, it is possible to rank high even without keywords in the URL but all being equal, if you have keywords in the URL (the domain itself, or file names, which are part of the URL), this gives you additional advantage over your competitors. Keywords in URLs are more important for MSN and Yahoo! but even with Google their relative weight is high, so there is no excuse for having keywordless URLs.
9-Backlink spamming:
It is a common delusion that it more backlinks are ALWAYS better and because of this web masters resort to link farms, forum/newgroup spam etc., which ultimately could lead to getting their site banned. In fact, what you need are quality backlinks. Here are some more information on The Importance of Backlinks.
10-Lack of keywords in the content:
Once you focus on your keywords, modify your content and put the keywords wherever it makes sense. It is even better to make them bold or highlight them.
