Depends on the subject. You have to be more specific I'm afraid but normally past papers, looking at the specification directly and making brief notes with cue cards is what I would do for a history.
There is a wide scope on revising. I occasionally use YouTube and affiliated sites to my course, I also use Get Revising to condense down my notes and then I make essay plans by finding questions specific to each section of my specification to ensure I am able to apply my knowledge. This is my example for a humanities based subject.
For a subject like Maths, I'm currently improving my revision techniques, so I would suggest past papers, topic papers, cue cards for formulas and just constantly practising tbh. Use YouTube to find a real answer for a method as some can be seriously hard to just read and apply. Asides that you could use a checklist and ensure you cover the broader topics. Normally checking the examiner report is really good for humanities and even Maths as you can spot mistakes etc. Math techniques i suggested can apply to Science
Therefore, without any real indication I've given a broader view but if any of the above is helpful that's good and if not, suggest the type of subjects you're doing and it'll help. Good luck.