What are your competitors doing? Where are they advertising, and what business driving searches are they capturing?
Explore all the possibilities, determining what makes people buy from you now in order to find the best paid search methods to find new customers.
Build highly effective search engine marketing campaigns, from strong text ads for search, to beautiful display ads (graphics) and remarketing programs.
Look at the results. Every. Single. Day. Do more of what works, and less of what doesn't.
Always be testing! As well as a campaign may be performing, are you sure it couldn't be even better? A/B tests are easy, effective, and necessary.