Philosophy, Psychology, Linguistics at university

I'm planning on applying to University of Oxford and St Andrews for PPL with Russian, French, Maths, English lit and Philosophy A levels.
Does anyone have any tips on reading I can do to get a head start for the course?

If this is a serious post and not one of those "I only have four Nobel Prizes, will Cambridge even look at me?" posts, then I suggest that you focus on your A levels for now. You might unwittingly have placed a needless obstacle in your path by taking five subjects.

I'd suggest just taking three A-levels, as that's all that is required and doing extra A-levels won't give you "bonus points".
As for exploring the subject, just read around the areas of your interest in those fields. Bear in mind typically you will just study two of the three of those subjects at Oxford as I understand (some do take up the third in second and third years). I'd suggest reading around some linguistic theory to get a feel for what that is - Oxford linguistics is pretty strongly seated in the generative linguistics theory tradition as I understand and doesn't include as much "applied" linguistics (I think their sociolinguist actually left recently), aside from the philology/historical linguistics set there. Syntactic theory and such is pretty abstract and may not always be the first thing people think about when applying to a linguistics course (but it's a pretty central feature of the field)!
You may want to also consider e.g. Edinburgh's cognitive science degree which covers those three fields plus CS (the MA version puts less emphasis on the CS side I believe).

I'm not talking about acceptance, I'm talking about what kind of textbooks and background knowledge of the course will help me educate myself more on their curriculum for my personal interest.
Also my school requires 4 a level subjects and I'm doing russian out of school because I'm a native speaker so it's not really an 'obstacle' as you have inaccurately put it.

English a level is different to a language a level... I assure you that any fluent english speaker would be able to complete the a level if it was on the same level as russian or any other language for that matter with little preparation which is why I did it a couple years early. I apologise for any confusion!

You said "I'm doing [russian] out of school". Now you say that you did an A Level in Russian a couple of years early.
A top tip: Oxford Dons all have Military Grade BS Detectors.

This is not a courtroom Stiffy?! 😀 lol

I'm not talking about acceptance, I'm talking about what kind of textbooks and background knowledge of the course will help me educate myself more on their curriculum for my personal interest.
Also my school requires 4 a level subjects and I'm doing russian out of school because I'm a native speaker so it's not really an 'obstacle' as you have inaccurately put it.

True, but those pesky Dons are sniffy about inconsistency as well as blather.

I understand what you mean! I’m a Chinese and the alevel Chinese is quite simple(i guess even some primary students can do it)but from what i know is that top unis like Oxbridge would not consider your alevel Russian as an subject since u r a native speaker. So i think maybe it is not that necessary to take the alevel Russian exam even though it costs u little time to prepare. And to answer ur question—there is booklist on the ox web for PPL. Not sure if you are aware at this stage—Applicants applying to ppl only choose 2 subjects among the 3, so u could just focus on the 2 that attract you the most