The following text is inspired by Gewin, Virginia. "How to write a first-class paper." Nature 555.7694 (2018). I made small adaptations for AS/A level Business and Economics essay-writing.
Keep your message clear
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Before starting to write, think about the message that you want to give to the reader: a clear message avoids misinterpretations
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Decide (before writing) about:
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the main message
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selection of data (from the extract)
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visual presentation (e.g. diagrams, …)
 
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the most important information should be in the main text/paragraph
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avoid speculation; instead use evidence-based conclusions (this includes scenario-building)
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conclusions should include a personal expert statement
 
Create logical framework
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In each paragraph:
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the first sentence defines the context
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the body contains the new idea
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the final sentence offers a conclusion
 
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The introduction sets the context (optional in short essays)
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The main body of your essay is composed of balanced arguments
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The conclusion contains the evaluation (e.g. judgement, advice, …)
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Guide the reader to the points where you want to give your judgement and advice
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Focus on the straight line that your audience follows from the introduction to the conclusion
 
State your case with confidence
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AS/A level students are often scared to make confident statements, especially in the conclusion/evaluation
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Economics and Business essays depend a lot on a strong confident writing
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As long as it is evidence-based, you should not hesitate to state your position with confidence
 
Think of story telling
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Always think of your busy, tired reader when you write your essay
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Deliver a paper that you would enjoy reading yourself
 
Aim for a wide audience
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Write in a way that is accessible to non-specialists
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Use terminology, but if it is very specific to your subject, define it to your reader