(That you can’t do much about)
Search engine optimisation isn’t an exact science. Google’s algorithms determine where your site sits in the rankings are complex and influenced by many different factors.
There are many things you can do to improve your rankings, however, there are a few things that will influence your website that you simply don’t have any control over. Here are just 3 examples of those things that will see your site go up or down the rankings without you doing anything.
All your competitors are also fighting to go higher in the search engine rankings. They are going to do things that will determine the order in which your websites are ranked. If you’re lucky then they could do something wrong and get penalised, which will push their sites down and your site up. If you are unlucky then they might splash out on a load of links from high ranking sites, pushing them up and you down.
It’s very difficult to find out exactly what your competitors are plotting until they have already done it and the damage has been done, so focus on your site and ways of improving the site authority.
3rd party sites
You need links from 3rd party sites to improve your rankings. However, the very nature of a 3rd party sites means you have no control over it. Therefore the 3rd party site that links to you will affect your rankings. You could strike it lucky and have a link on a site that suddenly has increased site authority, giving more weight to your link and increasing your authority. Or you could be unlucky and the 3rd party site will be penalised, rendering your link, at best useless, or at it’s worse all the outbound links on the site could also incur a penalty.
Google updates its algorithms all the time. Occasionally they have big updates, such as the famous Penguins and Pandas that saw huge shifts in the results, but they are continually making small shifts in the way search engine results are calculated. Not all these updates are permanent, sometimes they try something and decide it hasn’t worked. However, updates will cause fluctuations that can’t be explained by anything else. Your site may not be affected, if you have done everything correctly, but your competitors may be affected, causing your site to move around the rankings.
It’s best not to get hung up on minor changes, but to keep practising white-hat SEO in order to continually improve your site and to prevent it from dropping down the rankings.