For a doctor to increase his business he will have to consult and treat more patients, without patients a doctor cannot survive his/her business. Also if you (doctor) get more patients you garner more experience resulting in more patients. For this the doctor needs to differentiate from the competition i.e. other doctors and create his/her own USP. There are variety of methods a doctor can maintain Public Relations/Patient Relations. I have listed some key strategies:
 
No patient likes to wait and waste time at Hospital/Clinic. So the doctor needs to maintain an appointment diary and one day prior needs to call/message the patient about confirmation. This creates discipline for doctors and patients as well. I have myself witnessed patients confirming the appointments with doctor and the same vice-versa but the problem arises when the doctor travels to more than 5 locations and the doctor is stuck in traffic jams, leading to not checking the patients on time.
A doctor needs to maintain all the records about the patient, so the patient need not carry his/her records. Also on the patients next visit the doctor can check/inquire on the health of the patient. This is for the patients convenience after all they are the Clients. There are a variety of free software available like Google Health which the doctor can use: https://www.google.com/health/ 
Whenever pricking any patient with a needle/injection a doctor/nurse has to say sorry because you are hurting the patient. This leads to a very positive impact on the patients and the patient won\'t ever forget in their life that a doctor said sorry before hurting. 
Speak to patients and listen to them, they are already frightened. Console the patients and ask them to be positive about the treatment. Most often more than medicines and treatments a positive attitude helps to get cured from the aliment.
Call your patients after a week or two to check how they are feeling? Post-treatment hardly any patients will remember you, a call will make the patient feel important and they will refer you to everybody who is suffering from any aliment or disease. A patient satisfaction is very important to word-of-mouth publicity.
Whenever a patient comes to you for consultation for the first time give them a disease prevention booklet. The booklet will contain information on different diseases related to your specialization, symptoms, healthy living suggestions, etc. The booklet will also contain information about you, clinic addresses, consultation timings, appointment contact no, and how to reach clinic map. A Pharma company can sponsor the booklet, and can give their courtesy at the end of the booklet.
Attend CMEs and built contacts with other doctors, networking helps to build refferals.
Read newspapers, incase you find any story on surgery, disease diagnosis or anything related to healthcare, write a reply mail to the journo on what you think about the story and if possible suggestions on how the journo could improve and get more information, don\'t forget to signoff with your contact details. This helps to increase relation with journos and in future the journo might feature your quotes on a story related to this article.  
If you feel you have treated a unique patient or the surgery done was a very difficult one. Prepare a brief case study and mail to a journo, if the journo is really interested they will revert. On the other hand get in touch with a PR Professional for press coverage of the story. PR professionals will help to garner the best coverage in different publications.
Get your self and your clinic listed in local area directory and online on Wikimapia, this helps when the patient is doing Google on doctors available in a particular area.
Attend seminars and be a speaker of those seminars addressed at community levels in Rotary clubs, Church conventions, etc. Also be a part of free check-up camps this helps to generate patients leads.
 
Last but not the least, please do not try to scare patients and be honest in treatments, it always pays.