It all depends upon your personal inclination. If you are inventive, then inventing something, patenting it and then selling it to a major company can make you extremely rich.
If you are artistic, then writing top-selling novels (and they really do have to sell a lot) or writing a hit song could provide you with a fortune in royalties over a good many years.
If you are interested in financial matters, then it is possible to make a fortune on the stock market. The newspapers recently reported a schoolboy who made a quarter of million pounds in his spare time. His stock-broker had not realised that he was under-age!
Choose something which you are good at. Don't say that you aren't particularly good at anything - that's an I-Can't excuse!
Anyway, for every rich person who is a genius at their chosen profession, there are ten who are mediocre and yet BELIEVE in themselves.
I started this chapter by saying that it was the least important in the whole book. The next chapter, whilst the shortest, is probably the most important - read it carefully.