Doctors are often asked to make decisions which have no immediately obvious "right" or "wrong" outcome. Of course, as a doctor, you sign up to do this, and you won't always need help; occasionally though, there are situations that really give one pause for thought, and when a systematic approach is necessary to ensure you have covered all bases.
The most common of these approaches (to my knowledge) is Gillon's 4 principles. The way to use this framework is to work through all of the effects of a decision relating to 4 given principles, and use that as a basis to decide what is the best thing to do. The areas to consider are: beneficence (what good can come of it), non maleficence (what harm could be avoided), autonomy (does it give everyone a choice), and justice (does it do good for the greater community). If it is impossible to decide having done this because all sides of the argument seem to be equal, then more weight is given to autonomy, because there is truly no moral difference between deciding one thing or another, so taking choice away would make any decision unnecessarily immoral.
An example: as an NHS doctor, someone comes in and says that they have injured their elbow playing tennis, which is stopping him from playing the sport, but doesn't bother him otherwise. The only treatment is a very expensive surgical procedure. He plays casually with his friends, and would like to start playing again.
It would allow him to start playing tennis again, which also encourages him to live a more healthy lifestyle.
Any surgery carries with it the risk of not waking up from the anaesthetics, and also the risk of a complication. There is no 100% guarantee it will go well.
Allowing the operation gives him the choice to get it done, which is what he wants.
It would be unfair to give him an expensive operation on the NHS because the same service couldn't be offered to everyone with that problem, just on a financial basis.
Final decision: here, justice and the chance that it could go wrong far outweigh beneficence and autonomy. However, in a situation where he was a professional tennis player, it would add strength to the beneficence side, which would make it better to give him the operation. Most of the time, doctors have guidelines to help them as well as these frameworks, so you wouldn't need to do this, but every so often there are exceptions to them as well.