My #1 tip here is to choose facilitating subjects. These are the A-level choices that top universities want to see and I recommend picking at least 2 from this list. The facilitating subjects are: maths and further maths, English Literature, physics, biology, chemistry, geography, history, and classical and modern languages.
If you want to do a medical degree, choose chemistry plus either maths, biology or physics and then a subject of your choice from the list. If you don’t know what to, also go with chemistry plus either maths, biology or physics and a subject of your choice from the facilitating subjects list because this will leave many university degree options open for you so you can decide what degree you want later on.
Hope this helped!