what other methods can one use to increase search engine ranking apart from the various paid methods?

create google webmaster tools account
verify site ownership in google webmaster tools account
submit xml sitemap to google webmaster tools account
follow itemised instructions generated by google for your site in (wait for it) your

google webmaster tools account

cost $0.00.00000000000000000000
bit pointless to follow instructions from anyone other than google

Thanks a lot. I have done just that..

Following Google's Webmaster Guidelines that include Design and content guidelines, Technical guidelines and Quality guidelines are the Cheapest Search engine optimization method.