There is no definitively correct answer on revision. All students learn and revise in a variety of different ways.
However, my advice when it comes to History at A-Level and even during my studies at undergraduate level would be to dissect what applies to all students when it comes to succeeding in a History exam.
For A-Level, that would be:
i) Evidence - Primarily facts and dates.
ii) Analysis - the ability to apply these facts to an argument.
iii) Argument - being able to write persuasively.
These three skills are crucial to achieving an A or an A*. My tips for each one are as follows:
This is the 'nitty gritty' of History at A-Level and GCSE. The facts. Where it's won and lost on the day of the exam.
You are going to need to master dates, names and details. This can be incredibly dull, but if you nail your revision techniques, it honestly can be fun and you will be genuinely surprised at how quickly you commit information and knowledge to memory.
The way I did this: Revision cards.
Take some time to look through your syllabus. Get your textbook out and get writing. I believe writing down key facts, narratives and details is the best way to learn. Buy a pen that can select different colours to underline certain words, assign different aspects of revision different colours. For me, names were underlined in blue, dates were green and causes, effects and consequences that were crucial to different narratives in my history course were red.
Read them back to yourself. Speak these cards out loud, use acronyms and private (if necessary, inappropriate) jokes in your cards. As a tutor and a student that was in the position of History A-Level/GCSE students just a few years ago, I aim to give realistic advice: this will take time and effort, but it's worth it for the top marks.
This will come primarily from writing practice essays - your 'evidence' revision cards will also be very helpful. Basically, analysis means 'Fact X means that...' Although facts are crucial to succeeding in History exams, without the ability to connect these details to an intelligent point, they are useless.
Historians are an argumentative bunch. Examiners want you to make assertions. But, crucially, these cannot be empty assertions. They MUST be reinforced with evidence and linked to your analysis. Creating an argument and writing persuasively will also primarily come from practice essays. I am happy to take you through structure and examples.
I hope this helps!