Make sure there are no topics from year 10 that you still don't fully understand. In year 11 you often build on the year 10 work, and so will find yourself struggling a lot if you don't understand the year 10 work. And similarly, see if you can get ahead with things like reading your literature texts, as that will set you up well for next year...
Beyond that, I'd do maybe a couple of hours a week (better spreading this out, but if you can only do it in one chuck as too hard to fit it in otherwise, that'll also do!). Can be good to do it on a revision platform that tracks what you've covered / where you need to do some work, so that you ensure to cover everything briefly (eg Seneca Learning). Or make yourself a timetable to achieve the same thing of having touched on most topics by the end of the summer (and tackle the harder ones earlier, so that you don't run out of time for them)