Welcome to the online Intermediate Maths Club. You get to choose what to do.
There are strategy games to play to warm you up.
Then there is the weekly video about maths to watch.
Then choose any of the resources below to improve your problem solving skills. The Parallel links are for Simon Singh's website (you'll need to create a free account).
As a mathematician you should be reading around your subject from an early age (if you have Oxbridge or Russell Group aspirations). Simon Singh has an excellent list of book recommendations to whet your appetite.