White Hat SEO:
This is a legal way and accepted by search engines to increase a site's page rank.This includes usage of suggested keywords,topics,enriched content which drives traffic in a proper way.
Check Pushon.co.uk for few examples of black and white hat SEO techniques.It is always better that we do not follow the unethical practises.I am using the SEV service from Thewebpole.com which covers the major SEO techniques and helps in obtaining the desired pagerank.They cover many techniques like keyword and suggested topics,submit the site to over 100 search engines,submission to directories,sitemap creation and also provide reports which will eventually improve the pagerank and website traffic in an ethical way.