Bounce rates vary wildly across websites, but one of the uncomfortable truths of online design is that a large number of people will be hitting your carefully constructed content and heading straight for the virtual door.
People make astonishingly quick decisions about whether to stay on a site or not, and your job as a designer is to make it as appealing as possible for them to linger and look around. Poor layout choices, lack of search options and plain old irrelevant or low-quality content are all things that will send visitors packing.
From a design standpoint, you want users to be able to quickly determine which part of your website holds the information they seek. Keep the navigation friendly and label everything clearly to avoid confusion.