A-LEVEL Computer ScienceWatch
I would recommend looking at object-oriented programming and programming concepts to improve your programming skills. This will get you ahead of people who have done GCSE Computer Science. Many students at GCSE only know the basics of programming, this will allow you to get a step ahead of them, as these are
Also look into networking, databases, computer systems, and algorithms, there is a lot of content to learn, but it will be taught in lesson as well.