Keyword & Meta-tag Stuffing
Keyword stuffing/farming was and still is one of the most common bad practices. This is when designers over use keywords or multiple instances of the same word. The extra wordage placed emphasis on a particular word and would rank higher as a result. Related to keyword farming is meta-tag farming and is the abuse of over using meta-tags.
This practice was abused for a long time by coders and spammers. They built code to get a particular site to the top of the search results, even in cases where the site didn’t really fit in what the user searched for.
There is also the over use of internal linking. This is where a coder or programmer uses more than needed links to other pages contained within the site. This is an open door to stuffing the anchor text with keywords.
Divs in Left Field
Other ways included setting divs to either invisible or so far off the screen that you couldn’t view it. All of the text included many keywords that search engines would pick up on. Cloaking is another bad tactic. This is where the search engine sees something completely different than the user views.
NoFollow is used in forums and blogs to prevent spam bots from endlessly commenting and linking to a particular site. The problem with it now is people will trade links and one of them NoFollows the link so they get no love back. One person reaps the reward while the other gets nothing in return. Google put a stop to this by making sure both sites received no SEO love.
Black Hat Programming
Automated link dropping is when a programmer builds a program or bot to search out open blogs and or forums and drop links automatically. These are mostly deleted or can be NoFollowed but because the bot sends so many out the programmer is bound to get some links back.
Click Bots (click through popularity) are used to continuously click a link to raise the pages rank. This is now overlooked by most search engine algorithms.
Currently any form of bad practice that gets noticed will actually get you either kicked off the ranks list until you remedy the issue. So it may be easier to do it the wrong way, but in practice it’s best to take the time and do SEO the right way.