With offline marketing, it's very difficult to tell how people are interacting with your brand before they have an interaction with a salesperson or make a purchase. With digital marketing, you can identify trends and patterns in people's behavior before they've reached the final stage in their buyer's journey, meaning you can make more informed decisions about how to attract them to your website right at the top of the marketing funnel.
Another excellent guide is Google’s “Search Engine Optimization Starter Guide.” This is a free PDF download that covers basic tips that Google provides to its own employees on how to get listed. You’ll find it here. Also well worth checking out is Moz’s “Beginner’s Guide To SEO,” which you’ll find here, and the SEO Success Pyramid from Small Business Search Marketing.