Remember, a question in an exam is about what you know, not what you don't know. Make sure that you shape your answer to show off the breadth of your knowledge, while keeping focused on what the question wants you to demonstrate. Familiarity with your board's course specification and markscheme will help with this. The best thing to do is go into the exam with some general structural plans that you can rely on.

There are basic tips that will ensure your argument flows and adds clarity to your answer. For example, always open your paragraphs with a qualitative statement and close it with a mini-judgement backed up by evidence at the end. In fact, some markschemes specify that candidates cannot reach the top band if they do not make regular and nuanced judgements throughout their essay. You want to make it easy for a tired and busy marker to recognise you know what you're talking about and award you marks by setting out your argument as clearly as possible.

From personal experience the introduction to an essay is more important than a conclusion, as you should have made your central argument clear from the introduction and made judgements throughout, the conclusion is more of a summing up of an already apparent line of reasoning. That being said, if you're running out of time always prioritise reaching some kind of conclusion over continuing with your paragraph; again many markschemes specify that an ultimate judgement is needed for the essay to be awarded top-band marks. Although some teachers suggest you should not reveal the ultimate outcome of your essay in your introduction, I would personally recommend setting out your entire argument in an exam situation, especially if tie is a factor, the intent of your essay can at least be shown.

Once you've got these basics down, there are flourishes you can add to really stand out to the examiner and bump your grade up to an A*. For example, opening your essay with a salient quote from a contemporary which exemplifies the peculiarity of the era or phenomenon you're discussing or an event which you see as a turning point in your course.