From my experience, there are a few good ways to do that: make online self-service links prominent on your website and always offer them anywhere you provide your customer support number, integrate online help throughout key processes, promote Web and self-service resources in telephone hold messages, let call center agents notify customers of self-service options, and reply to email questions with the link to self-service content to re-enforce self-service availability.
FORBES: Eight Steps To Great Customer Experience (Part 1)