A lot of people would say study from day 1 but I find that is a little overkill and you'll only burn youself out.
I would advise you to stay on top of homework, notes and study for the class tests you have, this will ensure you are actually learning the material you are covering in class.
If you are struggling with certain topics for example an area in maths, then do take the time to figure it out.
Make sure you are actively listening in class aswell, ask questions if you are stuck.
In regards to revision I would say definitely start around christmas and make sure to do exam papers.
Good luck and I hope you get your course in a really good college.
Most importantly take care of yourself.
Each person is different... you need to be able to evaluate your self and see how much time you need to get stuff done. I personally started early this year (6th).
One thing that people dont pay egnoph respect to is FULLY and i mean FULLY understand what is being said in class... pay attention and make sure you understand and conprehend what topic you are studying... even if you forget about it later it will make study infinitly easier when times comes you start.