Remember that Queen Mary will support you in your transitionThe university is aware that students come from a background of different abilities and so there are modules which ensure everyone is up to speed, such as Mathematical Techniques Zero (MT0) which is unassessed and exists to ensure you have the skills necessary to effectively participate in other modules. That said there are of course elements which you will be unfamiliar with, which you can prepare for now.
Don't completely close your books over summerOne of the best things you can do to advantage yourself is to not let the skills you have developed for your A-levels or IB slip over summer. To get to university you have worked hard and deserve a break, but simply reading your revision notes once a week will ensure that the facts stick with you till September.
Get ahead on your reading If you are especially eager to get off to a flying start, you can begin reading into your modules now. The course landing pages are available online and you can get an overview of what the content of each module will be. By revising these areas you will give yourself an advantage over your peers and will make the harder topics significantly easier to grasp when you come to them. Maths is really importantOne of the key areas I personally recommend above all is your mathematical skills, which will be invaluable to you as a physicist. Laying a good foundation of maths knowledge will be crucial in grasping the concepts taught to you (hence the need for an MT0 module). As someone who went into this course under-prepared in mathematics, I can say you will make your first year ten times easier by picking up a calculus text book and familiarising yourself with the content. If you have not taken further maths at A-level or equivalent, it's a good idea to familiarise yourself with these methods as they will constitute a large amount of the mathematical content in your first semester.
You'll thank yourself laterIt doesn’t take a lot of time or effort now, but I can guarantee you’ll thank yourself for putting in a little time now when you see how much easier you have made the step up to university. Enjoy yourself this summer and try to find a few minutes if you can!