There are several worksheets available directed at planning your search. Here is one example and a guide for thinking through the PICO process.
Example | “In patients with heart failure from dilated cardiomyopathy who are in sinus rhythm …” | “… would adding anticoagulation with warfarin to standard heart failure therapy …” | “… when compared with standard therapy alone …” | “… lead to lower mortality or morbidity from thromboembolism. Is this enough to be worth the increased risk of bleeding?” |
From http://www.cebm.net/asking-focused-questions/
There are several levels of evidence, all related to the types of research and publications. Many evidence based resources incorporate evidence that ranges from the very highest level to the very basic level.