How do i get into Cambridge natural sciences (physics) from this point on.

Im currently in AS and live in Bulgaria, on my IGCSEs i got 7A*(math, add math, phy, chem, eco, english, french) and 1A (business). I havent done any olympiads or any other competition of that sort and its too late to start. I am taking Mathematics, Further mathematics, Physics and Chemistry as my A levels. I am wondering what do i need to do outside of grades to get into Cambridge. What kinds of extracurriculars/supercurriculers or tests should i take to increase my chances. Also, how do i decide to which college to apply. I dont know how to do the UKMT challenges because im from bulgaria and our school doesnt have them. I looked into doing CREST gold level but im not exactly sure how it works yet. SO yeah, im looking for suggestions on what to do to increase my chances to get in.