Determine who your main online competitors are. Research how they work, how they market and how big of a market share you believe they have. Sign up for e-newsletters, research their press releases and determine the strengths and weaknesses of each online competitor. You may even need to purchase something from them in order to understand how they complete their sales process.
The SEO starter guide describes much of what your SEO will do for you. Although you don't need to know this guide well yourself if you're hiring a professional to do the work for you, it is useful to be familiar with these techniques, so that you can be aware if an SEO wants to use a technique that is not recommended or, worse, strongly discouraged.