Search is useful when visitors know what they are looking for and the site contains enough varied content to make browsing difficult. It is not a cure for confusing navigation or weak page labels.
Look at the content first
Consider a resource library, product catalogue, documentation, job listings, or a large archive. Decide what users should be able to search, how results should be ranked, and what an empty result should say.
Measure the behavior
Review search terms, no-result queries, clicks, and completed tasks. Improve the underlying content when people repeatedly search for something that deserves a clear page.
For a larger content model, application planning can help define the right experience.