Always start your 12 mark essays with a brief plan, identifying what points you will be addressing in your description, and then what you will be addressing in your evaluation and any studies you will use. I would advise to take no more than about 2 minutes just jotting down your thoughts. You can then start your description which is worth 6 marks, outlining any information you know on the topic the question is based on. Then comes the slightly harder section of evaluation which is also worth 6 marks. You can structure your evaluation with three sections, Point - Example - Explain. For example you say your point (this theory is useful as it has supportive evidence), then your evidence (studies or facts you have learnt) and then finish with you explanation (linking your point and the study you have used to explain why this makes the theory more useful). I would advise doing three evaluative paragraphs. A conclusion that simply rounds up your points will help you gain more marks.