Given that Google now provides most Internet search traffic, last possible thing any site owner would want is to be banned from Google index!
With countless search engine marketing techniques being employed these days, and contrasting advice available all over web, it is well worth ensuring that you do not 'over optimise' your site or use any techniques which will result in Google penalising your site.
Although main rule would be to create a site which caters for your audience, provides quality content and contains meta information which is faithful to your site content, you should always optimise your site code to aid in your search ranking efforts, but this should be done in moderation, and in line with following tips.
Never, ever spam. This involves sending a large amount of unsolicited mail via your domain mail server. Although legality of mass mailing is a grey area, sites which do this deserve to be banned by every search engine.
Link Farms, or Free-for-all links pages exist solely to help listed sites gain higher search engine rankings. These are bad neighbourhoods and are frowned upon by major search engines. Obviously you can't control which sites link back to you, but you can ensure you don't link to link farms.
Now that so many webmasters are more obsessed with their Google Pagerank than amount of quality traffic they receive, link pages are fuller than ever. You should try not to place too many outbound links on a single page. If you do need to link to 100 or more sites, place links on separate pages.
Seen by many SEO specialists as probably thing most likely to result in a Google ban, cloaking involves creating one page designed specifically for search engines, and another which will appear for user. This is search engine manipulation at its worst.