19 years old, off to university for CS this september - what can I be doing now to set myself up for a career in finance?

New to WSO and I'm sure this kind of thing gets posted a lot, but I really wanna learn how I can get started in pursuing a career in high finance. 

I'm off to uni this september for CS, with Exeter being my firm choice and Swansea being my insurance choice. I've already missed the boat to go to a top undergrad target like Oxbridge, LSE, UCL, Imperial etc.

I suppose what I'm asking is, what can I start doing tomorrow, next month, next year and the next 5 years in order to give myself the best chance of breaking into finance. Would it be silly to start a LinkedIn now before uni? or to get some of the WSO courses done in the summer to apply to spring weeks & summer internships with? (if something like that would even help at all, I don't know).

Any guidance is appreciated. Thanks in advance :)