When writing a 12 mark answer in Psychology, I find it is most helpful to first understand the Assessment Objectives. In these types of question, you are awarded marks for AO1 (content) and A03 (evaluation). To gain all available marks in a 12 marker, I would recommend structuring it in equal parts of AO1 (explaining the study or concept) and afterwards implementing AO3 (writing down the relevant evaluation points).I always recommend students learn the 'generic' evaluation points that can be used as AO3 for nearly every type of answer just in case they struggle to remember specific evaluation points in an exam. Examples of these are: ethical considerations, sample size, validity.