The first part if focus. Is there one user set that you are ideally suited for -- solve their needs and build your value prop around that. Many times, companies want to serve everyone so they end up with a watered down value prop that end up appealing to no one. Ironically, a strong value prop works better even with the audiences it isn't intended. for. Take the Nisson Xterra from a product standpoint. It was marketed to be peope with an active, outdoor lifestyle. Nisson targeted the person who might strap on a surfboard and drive onto the beach. Now, most users end up not using it that way. But, because they built the brand and value prop around the active user, they establish a strong car brand that attracted a larger audience.

That said, people often misunderstand branding to mean that you have to always only be that one thing to that one audience, which is not true. Start with that simple value prop, and then develop more detailed communication.

The value prop itself should be able to be conveyed in a brief sentence. It should be true to who you are and what your organization delivers. And it should be differentiated from your other available options.

And, great if it is a psychological benefit! Nike's "Just Do It" is one of the great examples of a modern value prop. IBM had the informal, "no one ever got fired for buying IBM" -- a safety benefit for the risk averse. Find what you do really well that appeals to your core client base, then do that even better.

Hope this helps!