... and your visitors will keep coming back.
Your first time visitors dropped by your website because they might be interested in what you're presenting. Give them a chance to contribute and engage with you and other visitors and they'll keep coming back. You've probably heard of "Web 2.0". A major difference between version 2 and version 1 of the web is the potential for the engagement that creates community.
The goal is to transform visitors into community members. Examples of ways to engage members include:
Many other options exist. Some will be specific to the type of community you're creating. Others are external to your website - Facebook and Twitter being two common examples. Twitter can provide "instant updates" to members and get conversations going. While it may appear that Facebook with it's 800 or so million members is a natural for building a community it's proving to be far more challenging than one might expect.