This is a guest post by Cara Aley.
There is no faster way to negatively impact your SEO efforts than by subscribing to unethical SEO practices, otherwise known as black hat SEO techniques.
Google and other search engines are continuously evolving methods by which to identify and admonish violators of these unethical methods. The goal of a search engine is to deliver the highest quality search results to its users, so Google and others are constantly looking to weed out and penalize those attempting to cheat the system, and thus, cheat users of the search engine.
Here, we'll review some of the more offensive practices employed that search engines typically punish by negatively impacting your SEO.
Make sure your SEO practices really help people find what they are looking for - stay honest.
Don't link to low-quality sites or be linked from them
Bad back-linking is something you won't necessarily even know is going on, but you can and will be penalized for it by search engines. Having sites that link to you and have nothing to do with your site or its niche is seen as an unethical SEO method and can result in a penalty. Only linking to and from relevant sites provides the best user experience; hence, it is rewarded.
The best way to evaluate where your inbound links are coming from is to check Google Analytics (or whatever analytics tool you use) for referring links. You could also use any of these backlink checker tools. Then use Google's Link Disavow Tool to get rid of links to your site that are hurting its SEO because of their irrelevance. You can also simply ask those site owners to take links to your site down (but if they don't, Link Disavow is a great option for making that happen).
Don't build links too quickly
Google and other search engines know what a normal rate of building links is, so when you build links too quickly, there is a good chance your SEO ranking might shoot up briefly, but then shoot back down again once you are caught.
SEOptimise.com's case study "What Happens When You Build 10,000 Links in 24 Hours" digs deeper into the subject and actually shows that your ranking winds up being lower than it originally was due to penalization.
Don't put up poorly written, overly brief, or redundant content
Brevity is not king, as we may have previously been led to believe. According to Quick Sprout, "the average web page that ranks in the first page of Google has over 2,000 words of content." This is partly because there is a surprisingly direct correlation between length of a page's content and how many people link to it, as well as how many people will share the content!
So merely putting up pages of content with redundant or poorly written content isn't going to help your SEO (and it can actually have you penalized from an SEO standpoint).
This is an old technique but continues on and is one of the worse offenses in the land of SEO. Cloaking happens when your site identifies that a search engine is searching for it and delivers content different from what is actually on the website.
Pornography sites have been known to do this at times - they'll leverage search terms that have nothing to do with pornography and deliver their content to an unsuspecting visitor who thinks they are visiting a different page.
Purchasing older domains
Site owners have been known to purchase domains that are available and relevant to their own site, and then create links from those domains to their site. This can absolutely help with SEO but is definitely not a recommended practice.
In short, there's no quick solution for SEO that will wind up working in the long run. Pace yourself properly when building your site or blog's SEO, and focus on quality, not quantity, when doing so.
Search engines exist to serve their visitors with the highest quality content, and they are constantly improving how they weed out those who are attempting to cheat the system. Be sure you don't have strange and unrelated sites pointing to your own. Don't build links overly quickly - work at normal pace or risk penalization. Finally, and most importantly, generate content that is of the highest quality and value to your visitors. Google is watching!