12 Things NOT to Do to Improve Your Site's Google Page Ranking

1. If you created a new site, do not put ads on it right away - Google marks those sites as suspected "ad farm" sites and won't index them for a certain period of time (placing them into the sandbox). The common suggestion is to have your site up for one month with the content, before you can put ads in it. However there is no official word on that - so a shorter or longer period might be required.
2. Google gives high ranking to sites that have inbound links from other sites. But not just any sites. Those need to be sites with high ranking. That means that you can't just create a bunch of sites and have them link to each other and have your ranking go up. Neither submitting reciprocal links with link exchange sites will help. In fact it'll make things worse, as Google doesn't like "link farms". Sites linking to yours should also be relevant to your content.
3. Including links to social bookmarking services, like reddit.com, digg.com, del.icio.us, etc. (there are hundreds of those now and their number is growing) will allow your visitors to submit your site's links to those services in one click (e.g., see some of those at the end of this article). However most (all?) of those sites implement the link attribute rel="nofollow", which won't help your site's ranking.
4. Avoid duplicated content. There are many sites out there that spring up overnight, by copying content from other sites, buying pre-made sites, etc. Google detects those and penalises the guilty, by not indexing them. Instead of duplicating content, quote the relevant parts and provide a link to the original source. Also make sure that a single page on your site is linked to via a canonical URL, i.e. if you link to the same page as http://www.example.com/ and http://example.com/ some search engines consider that as duplicating content.
5. Avoid keyword spamming. Overoptimising and overusing key terms or using irrelevant keywords on your pages will negatively affect your site's ranking
6. Do not include invisible text. One can create invisible text by choosing the font colour which is the same as of the background, putting the text at the very bottom of the page, so that the visitor won't see it, and other ways. The idea is to include certain keywords multiply times to make the page appear more relevant. This technique doesn't work anymore, since modern search engines catch that trick and punish sites using it.
7. Search engines don't like dynamic pages that contain query characters like "?". Try avoiding those. You could try using rewriting rules to map good URL names to those dynamic URLs behind the scenes. Google definitely doesn't index pages containing "&id=" as a parameter in your URLs.
8. Do the redirects correctly. If you must move a document to a new location, the old location has to issue a 301 redirect code, which tells the crawler that the page has moved permanently. Webmaster have tried to use a 302 redirect (temporarily moved) to fool the users and redirect them to a different page than the one indexed by the spider. Though I can see how the spider can be fooled to not do the redirect, when it spiders the pages. This is because spiders can be identified as such before the page is served to them. So one could serve different pages to visitors and search engine crawlers. But don't do that.
9. Don't post too many links on a single page. Google suggests less than 100. When linking to other sites, avoid linking to sites with bad reputation. When you receive a request to link to another site, first go and check that the site is of a good quality and that it's of a relevant content.
10. Don't use unauthorised computer programs to submit pages, check rankings, etc. Such programs consume computing resources and violate their Terms of Service. Therefore if you still plan to uses one, you'd have to check whether it conforms with the rules or not.
11. When having other sites link to yours (inbound links), try to use different wordings for the anchored text. If it's always the same wording, search engines may consider those links as an attempt to raise your page rank and your site's page rank will be devalued.
12. Several sources indicate that submitting your site via "Add URL" to various search engines might be a bad idea. The premise is that if spiders can't find your site via other sites linking to you, then your site probably is not worthy their time. But this is only relevant for new sites.

Source: http://stason.org/articles/money/seo/google/12_things_not_to_do_to_improve_your_site_google_page_rank.html