Badly Researched Keywords

This is a common mistake made not only by inexperienced people, but, sadly by experts in SEO too.  The reason for this is that key words are subjective.  For you fish and smell may equate, but for another perfume and smell equates.  Subjectivity does not work in a business.  You need to get into the mind of the person using the search engine to see what equates for him.  There are useful tools on the internet that you can use.  Website Keyword Suggestion Tool is a great one and can help you get the right key word.

Neglecting the Title Tag

The title tag looks like this <title>.  This is the place that should have your well researched and perfectly optimized keyword.  This is one of the first things a crawler crawls over and indexes.  So, do not leave the title tag empty.

Using too many meta tags

This is something that was useful in the past but no longer is.  Already search engines have started ignoring them.  So stop wasting your time on them.

Using Images for Headings

Remember that search engines can not crawl pictures.  Title, Headings, Tags, Links etc are what search engines index.  Even if you think that a picture speaks a hundred words, remember, search engines can not hear those words.  If you want your website optimized for search engines, use headings, titles, tags and links.

Not optimizing the url

Do not ignore the url.  Get yourself a domain name related to your business.  If you sell spices and your domain name has spicenet or some such related name, it would be wonderful for your page rank.  If you do not get his at dot com, look for it in dot org or some other variant.  If will help get you ranking.  When your customer is searching for spice, your website is sure to come up first.

Using a flash website without a html version.

This is simple.  A spider can not crawl and read flash, so your website will not get indexed.  You need to provide html along with flash if you go for a flash based website.

Java websites

Yes java menus are wonderful for navigation but search engines do not read Java either.  If you are using Java, get your SEO expert to build you a sitemap with your links so that your links are crawled and indexed.

Useless backlinks

More backlinks does not convert into higher indexing by search engines these days.  Webmasters often mistakenly assume that this does, and go to link farms and backlink spamming.  This is a huge mistake and can get your website banned.  Get quality backlinks that are relevant to your website.

Not optimizing the content

You need to have keywords in your content.  Modify your existing content to insert keywords where they appear natural.  Highlight them, use upper case, make them bold.  In fact advertise your keywords in your website in this manner so that they get indexed faster.

Maintain your SEO

SEO is not a one time thing.  You need to constantly read about what is happening, tweak your website, and keep on optimizing it.  There are so many changes that take place and you need to update yourself and your website as per these changes.