company who will host your website, the big idea, the competition, the features, the featured product/news, information vs. on-line commerce, architecture, navigation, key words, design, copy, search engine optimization, website optimizations, Adwords, etc. etc. etc. Be sure that you guide your customer step-by-step through the entire process and, after you deliver your project, be certain that they know what to expect next.
There's much more to effective communication, but this is a wonderful start!