You have arrived here because you have a question that pertains to the effectiveness of a treatment (i.e. drugs, surgical procedures, hospitalization) or preventative measure (i.e. immunizations, etc.)
The first step is to map out your therapy question (the purpose of mapping a question is to facilitate a literature search). You must think about three things, Patient population, Intervention, and Outcome. Actually, what might help is for you to think about this as if you were actually designing a study.
Patient population - What population are you interested in? Is it patients in an emergency department, patients referred to a specialist, etc. What demographics like age, sex, race, are important. Do you want patients with a certain condition (i.e. asthma, or diabetes).
Intervention - Are you comparing one therapy vs. another, or drug vs. surgery, or one dose vs. another.
Outcome - Are you interested in mortality, return visits to the E.D., admissions to hospital, pain reduction, peak flow, etc.