In a best-case scenario, you will be able to find a high-quality pre-appraised information source to answer your question.
However, those are not available for all topics. Furthermore, you may also find it useful to appraise pre-appraised information. Once you figure out what to look for and where to look, you still have to worry about the quality of the material you find. You should always question the quality of the material you find. Remember, a poorly done systematic review is not better than a well done randomized controlled trial. On this page, you will find some resources to help you with appraising the material you find.
This site contains useful tools and downloads for the critical appraisal of different types of medical evidence. Example appraisal sheets are provided together with several helpful examples.
These calculators were developed by the Knowledge Translation Program in Toronto. They include calculators for statistics and Odds Ratio to NNT Converter.
This calculator can determine diagnostic test characteristics (sensitivity, specificity, likelihood ratios) and/or determine the post-test probability of disease given given the pre-test probability and test characteristics.
Population Prevalence, Sensitivity, Specificity, Predictive Values, & Likelihood Ratios
Predictive Values and Likelihood Ratios