One of the biggest mistakes (in my opinion) online is the hiding of content. This can be done in several different ways.
For example – email newsletters that aren’t also available on the website. Why expend all the energy of creating newsletters for only a certain number of people to view the newsletter. It would make a lot more sense to also add them to your website when you send them out. Extra pages of unique content for no extra effort. Brilliant!
Or try this – people who hide content behind a form. Search engines have difficulty finding pages that are only viewable by using a form to find them. Google can partially browse forms, but it is rather erratic and can misunderstand the forms. It is far better to provide an alternative method to find the content, either by using an HTML menu, or an XML or HTML sitemap.
These are just two of the more common ways in which content is lost to search engines due to bad decisions. While these issues are all easily fixable, it is important to recognise when you are wasting content, either by not putting it online, or by making it hard for search engines to index.