People doing essay based subjects at A level...

Learn how to write them (plenty of books and guides out there) and then practice. Take note of your teachers comments and advice.

You see that, vague f****** answers. I really don't have time for sarcasm.

I meant - how many extra essays they did...structure

Wow what an ingrate. How was I being sarcastic?

There is a methodology for constructing essays and people understand that.
They write good essays by following that+ understanding the subject+ practice.
If you want to understand the difference between grades, then you should look at the mark schemes for your subjects whicch detail what they are looking for at each grade and some of the model answers. You can then compare those with what you produce.

How many essays? It will depend on how good you are, but surely the measure is you need to do enough to improve to get the grades you require. That means keep doing them till you hit the grade and give yourself plenty of time to move from D/E territory to A. That means working with your teacher and getting feedback is important as they can point out what the weaknesses are. . D/e to C will be easier, then B and A will depend on knowing your subject and style. Focus on the basics first. Practice and exam papers are importnat becayse you need to get used to understanding whats being asked and familiar with various ways they can ask the same question.

That methodology should work.