Hi there,
Before university starts you should be given access to your student account on whichever platform they use. There you should be able to find any reccomended reading that your course suggests which you may want to look into.
Otherwise, I would say enjoy your summer. University takes in a whole range of students who studied different subjects on different boards so they will teach you what you need to know and dont expect you to be an expert. make sure you're taking a much needed break from working so hard from A-levels.
You can also prepare other aspects. Have a look at what things you might want to try - any societies, part-time jobs, academic projects that your university offers? What will you be taking with you - in this sense my biggest advice is less is more. There's no point in packing all your summer dresses if you wont be there for the sun. There are lots of places online which give good lists of things you'll need and wont.
Good luck with starting uni!
- Sophie (uni of Bath)