There are thousands of Plastic Surgeons in the world who do cosmetic surgery. Each one is trained differently, has a different esthetic eye, and experience. The ones who are Board Certified by The American Board of Plastic Surgery meet a certain standard of knowledge, but it does not mean they can achieve great results.
When I go to meetings, I can tell who is an artist and who is a technician in my field. The technicians are the ones who talk about precise measurements and protocols and absolutes, with algorithms for procedures and ratios that must be met. The artists are the ones who talk about balance and proportion and the variations of beauty from patient to patient. I like to think of myself as an artist who respects the traditions of technicians but relies on his own eyes to determine the final results.
To me, I like to achieve dramatic changes in appearance that do not alter the basic character of the person. Everyone should still recognize them after, and be left wondering what is different. If you get the harmony and balance right, even the most drastic improvement appears natural.
Part of it is also to listen to your patient, and communicate well to insure you are both on the same page with regards to goals. I tell my patients they do not have to choose the exact advice I would give as long as what they want is within the boundaries of good taste and normalcy.
How can you tell if your Plastic Surgeon is great? Talk to him/her, feel their personality, and see if the results are what you would want. If they can show you they have achieved what you want before, on a consistent basis, and seem to connect with you, it is probably a good partnership.