"My website used to rank great in Google, but now it doesn't. Why?"
I'm going to explain a few reasons this may have happened based on what I have previously discovered.
The first problem could be the age of the website. If the website is not updated regularly, it will run the risk of fading from Google's ranking. In highly competitive industries, like retail jewelry, if you don't add new content to your website on a regular basis you will lose ranking in search results. It's not because your information is bad, but simply because Google likes to show fresh information for competitive markets rather than content that could be written once and used forever.
Non-competitive industries, like agricultural research, might be able to rank highly for several years until someone else publishes the next study on cultivating banana seeds. Until then, that banana seed research will rank #1.
To figure out why your ranking dropped you should ask yourself how long it's been since you added a few pages of new content to your website.
The second problem could be the design of the website. We commonly call this the "User Interface" or UI for short. Outdated designs are clearly noticeable by everyday users. Google says that they will rank websites higher if the UI is easy for people to use. From my point of view I can't imagine how they determine this ease of use without having real people review the site.
On the other hand, if your design dates back 5 years or more then the programming code will also be old. There's a possibility that Google is using old code as a flag that demerits your website's ranking, or initiates human review. Regardless, old website designs do not age as well as fine wines. Your website ranking will lower over time, which is one reason I recommend a redesign every 18 months.
The third possibility is duplicate content. Have you ever paid a company to produce written content for your website? Perhaps you hired a blogging company or an article writing service? In the past, there were huge online businesses that specialized in collecting and reselling written articles. You might not know it, but the written articles on your site might be duplicated on hundreds of other websites.
Here's how duplicate content works now... Google only gives credit to the first website that was discovered to have the article. Any subsequent website will won't receive any ranking credit. The next time you hire a company to create content for you, you need to make sure you are paying for unique and original work.
The fourth possibility is spammy inbound links. This is probably the most-wicked situation to correct. Usually this happens when you've paid a company to provide "Link Building" services. Traditionally these inbound linking services would place spammy links throughout hundreds or thousands of online forums, comments in blogs, and build large blogging websites just to feed links back to you.
Sadly there are very little options available to you for correcting this type of problem. You could use software to show reports of those links, but you would have to contact every website and request those links to be deleted. It's easier to just abandon your domain name and move to another domain.
Now that I've given you a list of things to look for I do want to give you a closing caveat. Since I've been writing these Nuggets for 3 years now, it's quite possible that you are reading this at some far flung time in the future, in which case any or all of the items above are no longer valid SEO issues you need to look for... So yeah, thanks for reading on August 1, 2013 or August 1, 2016.