There are numerous things that make up this list of do’s and don’ts, some of which only the search engines know. But thankfully, there are some that the search engines have shared with us.
Hidden text and/or keyword stuffing
Hidden text is text that is visible to search engines but not necessarily visible to users. This can be done when text is embedded into a white background. Some webmasters use CSS to mark it as hidden or even remove it completely from the page. Keyword stuffing is when words (usually keywords) are used multiple times in a paragraph for the purpose of ranking. Often, these paragraphs make no sense and lack proper grammar, thus they don’t contribute any real value to the user.
Cloaking and/or sneaky redirects
This is when your site may be showing different pages to users than those which are shown to search engines, or redirecting users to a different page than what the search engines saw. If the search engines see this, they will apply a manual spam action to the affected portions of your site, and as a result, they will not appear in search results.
Buying or selling links that transfer page ranks is considered “unnatural” and is a big no-no. Links from irrelevant sites would also fall under the category of unnatural links. After a site is tagged for unnatural links, it’s likely their rankings on search engine pages will dramatically decrease.
Spamming is when you flood the Internet with many, many copies of the same message, in an attempt to force a message to people who would otherwise choose not to receive it. It’s usually totally irrelevant to what you are searching for, or interested in. Anyone with an email address will probably receive spam on a daily basis, hence the existence of spam filters. Spam can take on many forms. However, generally speaking, spam is commercial advertising. Get-rich-quick schemes, and penis enlargement products are popular ones that never seem to go away. Search engines have zero tolerance for spam, and it’s usually easily detectable.
For more on the do’s and don’ts of SEO, check out: https://blog.monitorbacklinks.com/seo/seo-dos-and-donts/