My own experience is that carefully reading the google documents which return when you do the obvious searches on how to improve SEO are very clear: do some structural work, be very clear about your sites underlying page relations, proffer keywords which contextually make sense, but do not try and game the system.
If you pay search engines money they increase visibility of your site. If you host adverts since they place adverts it increases visibility of your site in their systems because its a "virtuous circle"
If you attempt to use other mechanisms to direct traffic to your site which the search engine can (a) detect and (b) proscribe, you will be penalised.
What else is there?