1) Ensure that all of your assertions and statements are grounded in the literature and that you cite relevant academic or policy papers throughout. For Masters Level writing (level 11) you need to ensure that there is a strong grounding in the literature throughout.
2) Try and write your essay in three distinct parts, according to the criteria. It will make your writing easier to mark and you will also be able to check that you have covered everything.
3) Critically define your terms – wellbeing is a broad concept and you need to show that you understanding the implications that has for your essay.