Get in. Get out. Get on with life.
A successful Web site will make it easy for the users to get in, get or give the information they want, and then move on to another Web site (or better yet, to another activity in life). Users should not have to jump through complicated sign-up or sign-in procedures, see explanatory or introductory information, provide unnecessary or poorly justified data, or "learn" how to use a site.
Users won't browse or hang out in your Web site. Sure, there's Facebook, but your Web site isn't Facebook. It's not a destination; it's a resource someone can use to satisfy a known need RIGHT NOW. If they have a similar need again, and their prior experience with your Web site was quick and easy, you may be lucky enough to get them back.