Years ago, people used all sorts of tactics to rank higher. Today, Google is sure to de-index or penalize your website if you use any of these strategies. For individuals who have just started in the SEO field, these tactics should provide a good laugh for you.
Hidden Text - People would use white text on a white background to place popular keyword on their site without visitors noticing them. They would hide the name of a popular celebrity on their site 10 times, even though the site sold inexpensive furniture.
Scraping Content - Scaping content is outright theft of copyrighted material. Webmasters would steal web pages or entire sites and put the content on their own website. Now, it's okay to put a news feed on your site, however, 90 percent of your content should be original.
Comment Spam - Before Google introduced the no follow tag, blogs were full of generic comments, such as nice post, with a link to an unrelated site.
Negative SEO Attacks - Your competitors can pay crappy websites to link to your site with irrelevant anchor text. This happened to a travel website which couldn't understand why Google penalized them. Turns out, a competitor used the anchor text Viagra and linked to their website.
Selling Spammy Footer Links - To make extra money, webmasters would put links in their footer and accept payment for placing them there. Years ago, major sites, such as Forbes and The Washington Post, sold links in their footer and got caught.
Cloaking - Cloaking is having search engine crawlers see a highly optimized page, called a doorway page, while people who clicked on the link would see a different page. BMW actually got caught doing this and Google de-indexed them, but only for a few days. For more information click here https://www.reddit.com/r/SEO/comments/chlzp1/killerseotechniquesthatcankillany/.