What courses, books, and other information can I use to teach an employee to be an SEO specialist?

I own a technology services company. We host websites for our customers (as a small part of our larger services) and I'd like to offer our customers an SEO, marketing, and promotion service. Part of what we will do is provide regular blog entries on their sites, and we'll help setup their WordPress sites to be well positioned for SEO. I'd like to get an employee in my office up to speed to be the go the go-to person for the SEO in our office. Where can I point this employee to teach…