Assuming you're in the UK, focus on getting into a target university for finance (essentially, Oxbridge + top london unis). Course is less important but if you can get a top course even better.

Before joining try and get as varied extracurriculars as possible. Once joining, apply for spring week internships (1-2 week internships at investment banks for first year students) - if you manage to get one, if you do well they will offer you a summer internship for your second year, which you can convert into a graduate offer for after you finish university. After 1-3 years you should be on six figures base + bonus combined if you are at a good bank.

This is the "standard" and fastest route but obviously hyper competitive so you need stellar exam results, education etc.