Google Over Optimization can mark your site as a spammer site.

mostly i read in seo forum that you should put your keyword in title, h1, h2, h3 …, <i>, <b>.

well the truth - google can track you sites changes, if you try to hard to optimize your site and mostly you home page, google has a filter that put your site in a sandbox so your site cannot be found anywhere.

you can used h1 tag, but don’t try to optimize your keyword, the keyword can be in the h1 tag but not closed to each outer to much.

don’t changed to much your home page or changed to much your outbound links. if you changed it, it should reflect something new and useful for users, not for search engines.