Essay writing tips A Level

Hi,
My best advice is to have a go at exam papers, or just the essays of those papers, and when self-marking refer to the examiners report and see what they had to say about the specific essay questions. Then, and only then, refer to the mark scheme. It'll help create a mental image of what exactly an examiner thinks when going through someone's essay.
Also, your essays will be mainly AO3 marks, so it's important to work on explaining a concept but not repeating yourself. I strengthened this by discussing to myself a current situation in the world or a social issue and continued to extract my opinion out of my base statement until I could make it a complete justified viewpoint. I didn't bother writing it down, it'd take much longer. But, because of this, I built the mental framework in structuring my AO3 points, and then was able to much more easily segue it into a counterargument or to AO2 if I had a stem to refer to or back to AO1.
It's all about extracting and pulling until you get a fully fledged idea written on paper.
Hope this helps!