Your story sounds somewhat familiar- I did those subjects, apart from Further Maths. The moment I realized that I had more or less no revision technique came after my AS chemistry exam. I remember the night before I was sat on my bedroom floor with my books spread everywhere, in a desperate attempt to try and cram as much as I could for the next day. I ended up giving up on most of it, and just guessed a few questions that would be on the exam. Well, the next day, I was very lucky, since I could do most of the paper, but I decided I needed to buck my ideas up, since the chances of being able to guess all the exams was very slim.
For the science subjects, the way I discovered how to revise was to go through my notes after the syllabus had been completed (for maths, for example, we had about 3 months between the end of the syllabus and the exams) and make sure that I understood the concepts of the majority of the work. After reviewing a chapter, when I thought I'd understood it, then I'd attempt the questions for the chapter. I'd carry on doing this until I got through the course. Then, get your hands on as many past exams as you can, and practice actual exam questions-- you'll start to get the hang of how to solve the sort of questions that you will be given in the exam. (Note that this may not be the best advice on how to learn the material in your courses, it's simply what I found out, and practising past exam papers definitely helps you get better grades!)
As for geography, I can't really remember how I revised for that exam. I do remember writing out loads of case studies, etc, and then trying to write practice essays.
Finally, my time management was (and still is) dreadful! Basically, when I've got work to do, I have to get away from any and all distractions (e.g. computer, TV, friends!). I usually go to the library nowadays, since I can go there and not get distracted! Also, whilst taking my A levels, I realized that I was amazing at planning revision- drawing up extensive revision timetables, but I was awful at sticking to them! I think for this you just need to be tough on yourself.
Anyway, that's my experience on the matter; hope some of it helps!