Google are generally a great bunch! They do everything to ensure that the thing you are searching for is found instantly and includes at least some of the best websites for that term. Google are the online police...and without them, the internet would be anarchy. God bless them, right?
Search engine optimization means you want to make your website more visible to Google by gaining links while it is then in the hands of the internet community to decide your fate. However, there are (very bad, non-SEO) tactics that can really cause the faces of people at Google HQ to go all red, veiny, and consumed with rage - causing your website to slide dangerously down the search engines.
1. Paying for/selling links. Buying links is wrong, very dodgy, lazy, and the consequences of being found out can be disastrous.
2. Keyword stuffing - Keyword stuffing basically means cramming keywords in the meta tags or the main content on the web pages. It is important to get keywords into the content, but it obviously needs to be free-flowing and natural. Sometimes inserted text includes words that are frequently searched even if the words have very little to do with the actual content of the page, just in order to attract search traffic to pages featuring adverts.
3. Content farming - Used to apply to websites employing many freelancers churning out large amounts of low quality content only to increase page views. Google dealt with this and other crappy "made for Google" content through a number of updates to their algorithms. Whether published on your own site or elsewhere, Google still doesn't like crappy content.
4. Link exchanges - It looks unnatural (like Charlie Sheen buying bottles of water and salad in bulk), contrived, and Google will pick up on it. Therefore you need to use clever methods to get people to link to your website that wont require a link in return. Competitions are among the most effective method for this.
5. Comment spam - Commenting on every blog/forum in the World. Commenting on blogs etc can be a quick way to get traffic -- but you need to make sure that when you do get lazy and require instant traffic, then ensure that whatever you are posting is in keeping with the theme of the previous content and sticks to your target audience.
6. Article spinning - a semi-automated article rewriting "strategy" in which articles, original content or content from other sites, are reworded to give the impression of unique content. You couldn't get away with it in school with your teacher - and it is the same with Google. Effort needs to be put into article writing to make your work interesting and original.
7. Crappy linking -- Never link out to rubbish or spammy websites. If you wear nice suits and hang around with well dressed and classy people in everyday life, then you get treated with respect within society. Google operates in much the same way, giving more respect to websites with good online friends/links. A mixture of sites is good, but avoiding spammy sites is essential.
8. Cloaking - For example, a music website could buy the domain name "albumreviews.com", then you stuff that home page full of keywords, to perform well in the search engines, then you redirect that page to the music website.
9. No text -- Using lots of Flash or Javascript only? You utter mug! This is SERP suicide. Google loves good old-fashioned text and Google struggles to index Flashs weird methods. Why make life difficult? This won't tick Google off, but will definitely lead to Google turning their noses up at you and perhaps labeling you as mentally defective online amateurs. Who knows
10. ....
Can you think of a #10 that really messes up your chances for a successful relationship with Google?