How we increase product sales by SEO ?

[Justin]

1.keyword research
(what's getting the traffic? what's easy to rank for also,20 keywords or less you don't want to over do it)
2.onsite optimization
(internal/onsite keywords in script pages and post categories permalink's/SEO friendly URLS ).
2.a. keywords in titles at the beginning of the page roughly 3% density or less throughout, all articles are free from grammatical error and 350 words plus
3.submit to Google Yahoo and Bing for indexing,
(not as necessary these days, but still worth doing )
4. contextual do-follow back links involving your keywords from high page rank websites (pr 5 and higher)
(quality not quantity)
easily done with article submission

resources

hubpages.com pr 7
squidoo.com pr 7
technorati.com pr 8
buzzle.com pr 6
ezinearticles.com pr 6
make sure they are do-follow though some directories may not

there are lots of other things you can do but that is a good place to start