Do Not
List keywords anywhere except in the keyword meta tag. Text must make sense everywhere else on your website.
Use the same colour text as your websites background colour. This has often been used to try and trick search engines, however search engines can detect this and will penalise you.
Use the same tag more than once. For example, using more than one title tag. Search engines see this as spam.
Submit identical pages. Duplicating a page of your site and then submitting each one to the search engines is considered as spam.