Hi, physics is by far my strongest science so I'll help you out
What I'm doing, as dull as is sounds, is literally handwriting the specification except for the bits where it says 'explain why...' I'm changing that to the actual revision guide/bbc bitesize explanation. I'll then get to the end of one unit, and read through it all again and highlight the really important stuff, then I'll do a past paper but only the questions of the units I've just revised and stopping when it gets to the start of the next one. I'll then mark it and note down what my weaknesses were in order to later come back to them. I'll then do the next unit etc.
When I've done the paper completely I'll have a mark out of 60 similar to if I actually sat that paper.
After a while (usually the next day) I'll do a full past paper in exam conditions and then mark it - I tried to get the 2015 ones as best practise. Managed to for chemistry didn't for biology but I'm trying for physics! If not then I go really old (Jan 2012 usually) as we've done all the recent ones at school so it won't be accurate. I'll then mark it and write down all my weaknesses.
Then I'll go over my weaknesses again to make sure that I've got them sorted.
This usually happens the day before my exam for the first bit, then the last 2 happen on the day of the exam. However I wouldn't recommend leaving it this late as it is not a lot of time at all and relies on you having an afternoon exam which might not always be the case.
Hopefully this has helped, this is how I do it and it might not suit everyone.