A question often asked of SEO experts, is what is The Best SEO trick, or the best seo tactic, or the best seo tip - the fact is though there is no best trick or tactic, but there IS, I believe, a best SEO strategy.
The best SEO strategy in my opinion, and experience - is a holistic white hat SEO strategy.
The dictionary definition of holistic is:
"of, concerned with, or dealing with wholes or integrated systems rather than with their parts"
Holistic SEO simply means that you work on everything, the whole system - not just parts.
Many people involved in SEO, do not work in this manner - it's not uncommon at all to find a website that has had a lot of SEO work done in parts, but the website isn't doing nearly as well as it should be due to very important parts being completely missed out.