I CBA to type this out, just follow these steps:
1) Start ASAP - The earlier the better
2) Aside from student loans - Manage and pay off all credit card debt
3) Have an emergency fund - Money that will last you a couple of months
4) You need 5 accounts - Checkings (Current), Savings, Investments, Emergency and Bail Money
I'm joking about the last account (but who knows), but with your investment account, you need to ensure you don't need that capital for at least 3 to 5 years. Don't try time the market, I know what you're thinking.
You can literally even start with £10 by buying fractionally or even putting it in an index fund. But in my opinion, the sooner the better.
Look into a broker to use - Trading212, Vanguard, Plus500, Interactive Brokers, Charles Stanley Direct, Hargreaves Lansdown, there's loads, just research and decide. Bearing in mind some brokers have regulations, read the damn fine print. Now that this intro is out the way, go run up a bag my G.