All I can say is make sure you do well in the interview. I know people with exceptional exam grades who have not been accepted, simply because they did not perform well in the interview.
I don't know whether this helps or not, but also try looking at application statistics on the Cambridge website - some colleges get a lot more applications for certain subjects than other colleges, so this could be something to bear in mind when you make your application.
Another thing is the personal statement - from my experience the best thing to do is to focus on the subject, not how you're a member of the sixth form committee or what you've done outside your studies etc (unless its related to the course in question). Yes add 1 or 2 lines at the end how you enjoy sport and/or music, but be careful not to go on. Also its important not to come across as big-headed or arrogant in your personal statement.
Hope this helps