From a complete rebuild to some simple tweaks, websites today must be maximized for the user experience. Things change...and so should your site. If you find you're not having customers come back frequently or buying different things, this is something you should look at.
Email marketing in conjunction with an effective website is the most effective strategy to get customers to buy more. Customers today expect to be contacted. When they don't hear from you, they forget about you.
Search Engine Optimization (SEO) is more like rain than a fire hose. It is a long-term strategy that intends to bring consistency in your business by making your website easier for customers and potential customers to find.