Well, firstly have great GCSEs and A Level predictions.
Think about engaging in a range of super curriculars (extra curriculars not worth more than 1 sentence - with four being in the relevant skills gained from them more than the activities themselves) such as essay competitions, reading to extend A Level study and areas outside of that, maybe podcasts or lectures or visits for variety. Don’t list these but explain what you learned from them, ideas they expressed, debates raised and how this led to you seeking out further resources and your tentative conclusions on areas of controversy.
Think about factual content but also historiography and perhaps issues of studying earlier and later history.
A good start is a short paragraph about enthusiasm and A Level course topics which aroused particular interest and wider reading. Then a longer paragraph about other areas of interest and what you’ve engaged with and thoughts on the ideas. Try to make links between resources and ideas to show you can make connections. You might have a sentence on relevant extra curricular linking them to historical skills. Finish with a conclusion coming back to your enthusiasm for History and what it is about degree level study that enthuses you. It’s like an essay - your into and conc are the start and end of a circle that ends at the same point.
EPQ based on History can be useful for PS. Likewise your NEA can be handy too. An example extended piece of writing outside of the course content will look good. Awareness of historical debate on some topics and continued and ongoing engagement with a topic or theme shows interest.
Presumably you have summer yr12 exams to come. You need to actual to get the best possible predictions.
What’s your GCSE profile and what do you hope for in terms of PGs?
It’s good to be thinking about it now. You’ve plenty of time for listening, reading and engaging so you can have an excellent PS..