In order to win your medical malpractice case against your doctor, you must prove that your doctor was negligent. In order to show that your doctor was negligent, you must prove two things.
First, you need to prove that, in a given situation, every doctor is supposed to act in a certain way. For example, if you want to sue your doctor because you told him you were allergic to a certain medication, and he gave you the medication anyway, then you need to prove that every doctor should know not to give a patient medication that she's allergic to. In essence, what you have to prove is that there is a specific standard that every doctor must measure up to.
Second, you need to prove that your doctor failed to perform well enough to measure up to the standard applicable in your scenario.
The only way to prove these two things is to hire a qualified and well-respected medical expert. You need an expert witness to explain to the jury how it was your doctor messed up. In fact, in many states, including California, you absolutely need an expert witness in order to win your case. Here's an example of one source of medical experts. Here's another example.
Knowing that you will need an expert witness to win your case, you should also realize that you need a lawyer who knows the best medical experts. There are many types of experts out there and not all experts are created equally. You want to make sure your expert is better than the expert your doctor is going to have testify.
You need a lawyer who is familiar with the best medical experts in your area. That plays a big role in winning your medical malpractice case. To find a medical malpractice lawyer near you, look for your state on the left side of your computer screen.