It can happen. You spend hours upon days, days upon month doing everything you can to make sure your website has every opportunity to be ranked by Google only to wake up and find that you have been dropped -30, -60 or even worse BANNED! Here are six things to keep in mind when optimizing your site.
1. Duplicate Content
This is a biggy. Google hates duplicate content. Be sure everything you write is unique. If you have a page that is getting dropped or banned consistently, copy and paste a sentence from it into a Google search box and see if it comes up anywhere else. If so, REWRITE IT. If you feel that someone grabbed your content report them: www.google.com/dmca.html
2. Doorways, Cloaking and Redirects
Don't do it! These are keyword stuffed pages that are designed to attract search engine spiders but are otherwise meaningless to web surfers. If you are getting away with it, STOP! It is only a matter of time before Google comes knocking.
3. Hidden Texts and Hidden Links
This is a practice by where the web designer will again stuff pages with meaningless content to attract spiders but use colors that make them seem invisible by matching it to the background color. Bad Golf, do it an pay the piper.
4. Keyword Spamming
Keyword spamming is stuffing the meta tags with keywords that don't relate to the content. At this point meta tags are becoming less valued every day but it is a bad idea to try this as all the keywords in the meta tags should also show up in your page content.
5. Good Link Bad Link
It use to be the more link backs you have the better. Not the case anymore. Google looks for quality link backs (or reciprocal link) from quality sites that have link popularity not gained from link farms.
6. Bad Template Websites
There are some website companies that sell template sites that are not SEO freindly. Some of these sites are highly dynamic using replicated content or use frames. Before using a template company ask about SEO and look to see how some of the other templates rank.
(thank you to Gareth Dirlam for 7 and 8)
7. Automated Queries
Automated queries are queries made using some sort of submission software. In some cases this is allowed but not without express authorization from Google. So unless you have permission, don't do it.
8. Keyword Stuffing on the Content Area of Your Page. see my post on keyword stuffing
Loading Anchors with keywords (its not just the meta tag that gets stuffed) will get your page penalized.
I have been getting a lot of response to Keyword Stuffing, so I wrote a seperate blog on it, hope it helps.
http://activerain.com/blogsview/431535/Keyword-Stuffing-Bad-Bad
Thanks for the tips...I have 2 different blogs and I often post the same article to both blogs. I'll drop that practice.