Back when I was teaching design, we had an assignment that had students draw an object as a self portrait.  It went like this...choose an object (let's say clock), then don't stop there, think about what kind of clock represents you best.  Are you a stop watch, a grandfather clock, and alarm clock, a wrist watch? If you're a stop watch, are you digital, old fashioned, metal, plastic?  Each has a distinctive personality and we were asking them to think more deeply about how they choose visuals for their designs.  

You can use this same technique when deciding what images to include on your website.  Say you want images of nature because your products and services have a natural quality.  Ask yourself the following questions...What aspects of nature best represent my business (trees - grounded and strong, flowers - vibrant and colorful, leaves - life transitioning, etc.)?  Then go deeper, say you choose trees.  What kind of trees best represent your message (evergreen - everlasting, redwood - tall and wise, flowering trees, newly budding trees, old winding trees, etc.) Think about the qualities/personality of the object itself as well as it's shape, line, and color. Is your message logical (perfectly pruned and angular bonsai tree) or free flowing (natural and bushy tree) Continue this process, going deeper and more detailed each time until you have images that truly represent your business and your message.