English Literature- how do I revise?

You could identify some key scenes, key quotes etc, and look at past papers like you've been doing. What I find useful is to read examiners' reports, which show what they're looking for and what high-scoring pupils did to get the grades and why other students didn't do so well, then try and apply that to your own essay writing.
if mind maps don't work for you, don't use them as they won't be effective revision. When you look at past papers, look at the type of questions they ask as they are often quite similar year on year, and see what the question asks you as well.
Good luck with your exams

Do you know how I could test whether my revision technique is effective or not (e.g. mind maps)?

Don't be disheartened, try some more past papers! You can always post them on here for some feedback this time too, they're really the best way to revise. It's almost like cheating if you've already done an exam in revision that comes up for the test.

The thing is though, I'm doing the newer English Literature syllabus (from 2010) so I only have 6 past papers in total

However, I find this to be extremely tedious and it takes me about 2 to 3 hours to create one mind map and I am not even sure if it is "working" for me.