This is the basic tenet of all marketing. If you do this, you will usually make the right decision. About your products, your services, your image, your position, your marketing, your advertising, your website.
Take the time to identify the person that is your primary target market. Describe that person. Write down a full description. Then think about the person you described every time you make a decision about your product or your advertising.
In PR you also have to think about your clients’ customers.