At Nexus, a doctor writes about the problem of miscommunication between doctors and patients, pointing out that the misunderstandings can occur on both sides.
A commenter (herself a physician) makes an excellent recommendation, based on her experience in helping her elderly parents as they visit their primary care doctors: she writes out her parents' medical history, including current medications and dosages. She lists the main complaint, any related complaints, how long the problem has persisted, the tests that have been done, and the results. The parent takes this sheet to the doctor's office, so it helps to guide him in his assessment of the problem.
Being a physician herself of course makes it easier for her to do this, but it can be done by any reasonably knowledgeable adult.
It would also be helpful for the doctor to do the same thing: prepare a written sheet, providing his diagnosis (and an explanation about it), his recommended treatment, and when to return for followup, that his patient can take with him to help with discussions with his family.