To appraise a systematic overview, there is a series of questions that you must answer.
First of all, was the study valid?
Did the overview address a focused clinical question?
Were the criteria used to select articles for inclusion clearly stated and appropriate?
Is it likely that important relevant studies were missed by the search strategies employed?
Were the assessments of the studies with respect to inclusion criteria reproducible?
Were the results similar from study to study? If heterogeneity was present, was it clinically significant?
After thinking about the above questions, Is there a FATAL flaw in the study?
If there is, then toss this study and go onto the next one. If not, continue the appraisal.
What were the results?
Were the results pooled, and were the confidence intervals sufficiently narrow to eliminate ambiguity?
Are the results applicable to my patients?