It sounds simple, but you need to know the book really well. For example, I think loads of people would find it really easy to write an essay about Harry Potter if they revised the quotes because they love the books and the characters and are just so familiar with them.
English literature revision is the complete opposite of any kind of maths and science revision - you can't learn everything they will throw at you. In a maths exam, you know what topics will be on paper - there are bound to be quadratics and simultaneous equations etc. So it can be quite daunting to revise for a paper in which they could ask you to analyse something you have never thought about before.
Revising EfficientlyWhatever book you are studying, read it regularly and use thin post-it notes to mark pages with the best quotes and quotes that can be applied to multiple themes. Make mind-maps of quotes and ideas per theme. These will either a) help because you have revised the specific theme/character they are asking about or b) help because in making these you learned the book really well and can answer questions about something else. Approach it with an open mind. Then, once you feel you know the book really well, start looking anywhere you can for practice questions on your set text.
General TipsSome good acronyms (some you may have heard of...)
PEAR - Point, Example/Quote, Analyse and Alternative Interpretation, Relevant because... (link back to point)
SKITTLES - Summary, Knowledge, Imagery, Themes, Tone, Language, Effect on the reader, Structure
Examiners love their alternative interpretations - if you can effectively justify your point and it is unusual and outside the box, it will make your essay stand out.
Comment on words and phrases rather than sections - sometimes focus in and make a big point about subtle details.
Research SHC (Social Historical Context) so you can comment on what the writer might have been alluding to - for example, Macbeth was written at a time where there were a lot of people who did not like the King of England and were plotting against him (including the gunpowder plot) - it is no accident Shakespeare wrote about the downfall of someone who murders their King.
Before starting any essay, it is a good idea to devote 5-10 minutes planning it. It sounds risky but is honestly so helpful - you get all your ideas and the structure together before starting the essay and you don't end up with a mid-exam panic because you have run out of ideas.
I hope that helps a little! Good luck!