Many routes actually, though everything requires luck really (being the right person at the right place and at the right time):
Sensible suggestions
1. Going on Dragon's Den with an idea to start up a business or make an existing business larger
2. Start a YouTube channel and develop your content over the years
3. If you're a person who likes doing something new everyday and wants to explore places when needed, you can try acting or modelling and see how that goes
4. Social media fame (easy to do nowadays)
5. Audition for talent shows/singing contests if you have what it takes
Unlikely or dumb ways of getting money but people still do it anyway:
6. Winning the lottery like someone else said (chances are pretty slim but never impossible)
7. Be either an utter tw@t or be fake enough that you gain enough interest from the world for people to obsess about you aka danielle bregoli (that cash me outside girl) and the kardashian/jenner families.
8. Marry a rich person.
9. Become a drug lord and enjoy a luxurious prison sentence if caught.