The subject of Search Engine Optimization (aka SEO) is one of much debate. Some of the information found on the web is valid, other pieces were valid in the past but are no longer valid and still other information was never true to begin with.
Here are three common SEO myths:
1. It's impossible to outrank a web page with a Google PageRank higher than your own
As "PageRank" is specific only to Google, it won't affect your search engine rankings at Yahoo or Bing. Even on Google, the PageRank indicator only plays a minor role in determining search engine placement and is certainly not a critical factor.
If you do a few searches on Google you will find this to be true. Within a few minutes you'll likely find a page, with a lower Google PR, outranking a page with a higher one.
That should put this myth to rest.
2. SEO is a one-time activity... you simply "set it and forget it!"
It would be great if this were true but it's not. Effective Search Engine Optimization requires ongoing work (and maintenance) and if you discontinue your efforts, you'll find your rankings slip over time.
This is especially true when it comes to link building. The search engines monitor your inbound links and if they come to a sudden halt, they assume your page is losing its relevance.
3. Each page should have a keyword density of 3-5%
This may have been true in the past but it's not any more. You should see that your targeted keyword phrases appear somewhere on your page but you don't need a calculator.
Instead, you should concentrate on writing content that will be found valuable by your visitors. After all, the search engine robots aren't likely to buy any of the products/services you have to offer.