There is no one big secret to making money but there a few ways of getting richer, some in your control, others completely arbitrary.
The secret to making money is working hard
Perhaps the dullest and most predictable of options when it comes to making money. Simply, put in the graft. Work on your will power. Build up your stamina until a 12 hour shift feels like a walk in the park. Work till your fingers bleed, then work a little more.
Inherit money and get rich
Unbelievably, this is even harder than outright toil. Be born with a silver spoon and inherit millions, if not billions from your family. Watch out for inheritance tax though - you might want to invest in a clever lawyer.
Being brave in order to make money
Or...be reckless! Gamble what you've got to make more. It takes steady hand and a fearless attitude but some people have made so much money through outrageous investments that they will never have to work again.
Get tight to stay rich
The last way to make money (or rather to make money last) is to just never spend it! Get tight - don't go to the bar, wear your clothes 'til they're rags and try your very best not to ever have children. Life may become rather grey and lifeless but at least your bank account will be healthy.