In this post I'm going to talk about A level choices and how they affect your chances of getting into Cambridge.
Firstly, when I applied was before the new A* grade had been brought in and so the top A level grade was an A. Back then the standard offer from Cambridge was at least AAA. However, since the new A* grade has come in, offers will normally be at least A*AA and there has so far even been one case of an A*A*A* offer being made but this is not yet commonplace.
If you do get an offer, you've got through the toughest part of the selection process (in most cases) and you'll have from January until the summer to make sure you're up to standard on all your subjects to ensure you meet the offer. There are a few exceptions, mainly maths where you might get a STEP offer which is a LOT tougher than A levels.
With regards to which A levels to pick, Cambridge recommend doing 4 or 5 AS levels and then 3 or 4 full A levels. They say those doing 4 ASs will not be disadvantaged against those doing 5 however I would not agree with this. Overall you want your application to stand out as one of the best and doing more A levels helps with this. Basically 3 A levels is not enough. The average entry qualifications (before the A* grade) to Cambridge was AAAAa (4 As at A level and an A at AS level). This means you should be doing at least 5 ASs and 4 A levels if you want to be at the average entry standard.
If you are able to do more A levels then all the better but once you start going past 4 you need to make sure you're still going to have enough time to do interview preparation. I know multiple people who got in with 5As at A level and one who got 6As at full A level. Doing this many is not necessary but it does help you to stand out.
Doing A levels early also helps to make you stand out. For example doing all of one or even two A levels by the end of Year 12 will show your work ethic and motivation. It will also help to take the pressure off in Year 13 when you need to prepare for the Cambridge interview. I would definitely recommend this if you're able to do it.
I do not know what standard offers will be like now the new A* has come in, but it used to be the case that Cambridge said the standard offer was AAA but they'd do things like making an offer of As in further maths, physics and chemistry which is effectively a AAAA offer as you have to get an A in maths to get an A in further maths. AAAC offers were commonplace if you were doing 4 A levels and AAAEE was commonplace for 5 A levels.
With regards to subject choices, Cambridge provide a list of subjects that are recommended at A level when applying to different courses. For your chosen course, anything that is essential or highly desirable you should definitely be doing at A level if you want any chance of getting in for that subject. Different colleges have different subject requirements which may influence which college you choose.
When picking the remainaing subjects, you want to choose hard, difficult, academic subjects like maths, physics, geography, english literature and so on. You should not be choosing easy subjects like media studies, business studies, theatre studies. These are looked down on by people at Cambridge which you don't want.
In summary then, I'd recommend doing at least 4 full A levels and preferably 5 if you can manage it, all at at least A grade level, in hard subjects that are relevant to your chosen course. If possible, try to complete 1 or 2 full A levels by the end of Year 12.
