Mohammed - not sure if you mean 'how to write a critical review of an existing policy paper' or 'you want to conduct a research project that reviews a policy position'? Either way - I would argue that if you need to ask the question - it is probably best to avoid writing/conducting such a review in the first place. Most people that do come from an strong, established policy position.
Dean- I agree that making policies requires specific skills but then if we stop critically analyzing policies, we would sieze to come up with policies for the dynamic world we live with.