it really depends on the nature of the subject. I haven't sat an actual exam in a while., but I sort of studied when I was putting together my stuff for my honours thesis. I looked through all the notes I had written myself anywhere, I rewrote anything I still thought was important, I made note of anything I thought needed additional research and where I thought I would get that research from and then I prioritised what I had. With all the literature I was looking at, I tried to know what I was looking for from each text and only read that section and highlight the bits which were useful to me. I am quite lazy, but that method was effective and managed to get me to keep working.
I also scaffolded my actual thesis into lots of headings and tried to fill them in as I went along and then I cleaned up and made it all coherent and stuff, and I had about 4 people look over it as I was going along. I find working with headings and labelling the stuff I want to get done really helpful, it sort of works like a check list. Some of the other stuff I mentioned is not really relevant to studying for an exam