Don't see a psychologist, be a psychologist
I think it is interesting that BF Skinner, the most renowned behavioral psychologist the world has ever known, finished his career in advertising. He is not the only psychologist that found that the skills transfer nicely into the business world.
As a public relations psychologist, you need to figure out what makes people respond in optimal ways. Use the principles of group think to get the public on your "bandwagon". Use the principle of habituation and desensitization to slowly present pieces of unpopular decisions or actions. The more you know about the principles of psychology the better able you will be to work with the public's psyche and achieve your desired goal.
You can study this stuff yourself or you can take a class. Find out about the fundamentals of memory. How is it that the way information is presented influences the way that memories are stored? You should find this out if you are trying to create an impression, or a memory, in the public mind.
