Black Hat SEO Techniques
The search engines are in a constant fight against spam. Spam makes users unhappy. If users are unhappy they will stop using that search engine for their queries and the site will lose advertising dollars. That is why Google issued their webmaster guidelines to make it real clear what was considered to be "black hat" or spammy in terms of getting your site to rank high in the results.
If you use black hat SEO techniques then you taking a gamble. You might get some short term benefit by seeing your site rocket up the rankings, but once the search engines catch on to what you are doing you risk getting your site banned and losing all of your rankings as a result. So, what exactly can get you into trouble? Let's take a look.
1. Keyword Stuffing - Do not try to use your keyword over and over again inside the content of your articles. For this page I use the title "black hat SEO techniques" where it fits into the text. I don't repeat the phrase over and over again in sentences that make little to no sense. Keyword density is one of those factors that went out of the algorithms a long time ago. You want to write your pages with the user in mind, using language that is as clear and concise for them to understand as possible. Do not include a list of keywords at the bottom of your site or any of your pages. I saw this a lot around five years ago but those sites are normally no longer to be found.
2. Invisible Text - This practice is similar to stuffing because the invisible text is normally the keywords the writer wants the page to rank for. What you will see happen here is if a site has a white background, they will make add text to the bottom of the page that is white as well. This way it's invisible to the user but the spider's will still see it. The programmers at Google are smart enough to detect this kind of nonsense, so if you are using invisible text on your site then you will be caught and your rankings will suffer.
3. Linking Schemes - There are a ton of linking schemes out there and whether the tactic is classified as black hat or white hat isn't always clear cut, but is defined on more of a sliding scale. You aren't supposed to buy links, but there is a big difference between buying through a network where your site gets linked to buy hundreds of different unrelated sites and paying someone to include a mention in a relevant article. Do not build new sites full of thin content just so you can link back to your main site. Reciprocal linking is supposedly frowned upon, but only if you are including hundreds of links on one page, linking to bad neighborhoods, or exchanging with irrelevant niches. I haven't seen any problems related to reciprocal linking with sites in my own niche.
What tactics you employ to try and rank higher in the search engines is your own decision, but just remember they can and will penalize you if what you are doing appears to be spammy.