It's impossible to remember evaluation points for every possible essay that may come up on the exam, so it's a good idea to always think of what's covered in the Issues and Debates topics, and apply it to the essay. If we use the example of Milgram's study, you can use the gender debate to argue that the sample is limited to men and therefore andocentric, so we cannot make universal assumptions of female behaviour based on a white male sample. This also relates to the cultural bias debate as they were all white US men. Another really useful area of evaluation is the consideration of ethics. Did particpants all give informed consent? were they protected from harm? did they ensure confidentiality and privacy and given the right to withdraw? Were they unecessarily deceived and not given a suitable debrief? It's also good to bring in other studies and topics in from other areas that either lend support to the theory / research or are inconsistent with the findings. You can also have a think of the potential implications the research has on wider society, for example research into attachment could influence childcare practices, and research into individual topics could have potential implications for healthcare.