In the past companies designd websites with little regard to seach engine optimization. These websites were not used for generating leads, they were for the existing customer base. Today companies cant succeed online with this method. A successful search engine optimization strategy is neccessary for any business website to work.
The first component of success is a plan. In SEO this usually starts as a discussion about the purpose of the site. What do you want to accomplish with this website? There are many good answers to this question: brand awareness, sales, customer support, or build a community. Usually it ends up being a combination of these things. With a better understanding of what your goals are for the website you can start to work on the rest of the SEO strategy.
The rest of the plan will come from the other sections here.