Hi, While building links for a search phrase with quite some competition and over 12k a month searches, I noticed something interesting - Google started to play with the rankings. At first, (after building few quality backlinks by guest posting on different high quality blogs) my site ranked 18th for the search phrase I'm targeting. Obviously, I wasn't satisfied with the 18th position. The bulk of the traffic goes to the first three search results. I started to build more links. I did some social bookmarking links and a good amount of guest posting (11 guest posts). When the links got indexed by Google, my website's rank for the search phrase I'm targeting dropped. My site was on the 87th position for that search phrase. I was quite afraid that the drop was caused be the lack of backlinks with unrelevant anchor text (e.g. things like "read more", "here" and so on). In order to make the backlinks seem more natural, I wanted to build more links with unrelevant anchor text as well as change the anchor text of few existing links to something unreleated to the search phrase. However, I did not have time for that and for few days everything stayed as it was. Surprisingly, few days later, my site was on the 8th position for the search phrase I desired to rank good for. I found it quite odd and started to Google and read up on Google play (not the Play Store for Android, but the act of Google playing around with rankings of a website) and somebody actually stated that Google uses the play time in order to test the links, to see if they are natural or not. The idea is that if you start changing the anchor text of the backlinks while Google is playing with your site's rankings, it's a signal that the backlinks are not natural. Of course, like most things concerning SEO, this is just speculation. However, just to be in the safe side, I wouldn't recommend anyone to change the anchor texts of the backlinks while Google is playing with the rankings of your website.
If you rank at 8, why would you want to change what got you there? Duplicate what you have done with new links and content to improve your ranks further.
Build links naturally. Google can see when you're just throwing links and buying them from other sites. And it always fluctuates, my sites will hop from the first listing down to the 9-10 listing and then come back. I have even taken my site offline for almost a year and in less than a month it was in the same spot as when I left... Just keep your site fresh and not spammy, you'll be fine.
The most important thing you can do is stop gaming the system. Natural organic backlinks will very rarely be targeted. Google wants to offer the best search results, that's their sole intention. So, when they detect unnatural linking patterns they're prone to taking action. I would avoid questions like "how can I better game the system", and start asking questions like "how can I build natural, organic links?" More importantly I would ask "how can I build content that's actually helpful for humans (not robots) that they'll share with their friends?" Just my $.02.