Your question does not mention whether you want to know the secret to be rich money wise or be rich in life.
Secret to getting rich moneywise is Knowledge. If you have knowledge of things that you are capable of performing well then others, you are most likely to become rich. There are other books or people who will tell you all kinds of stuff about how to get rich, but it is really simple. Gain Knowledge to become rich money wise. Even if you want to get rich by selling drugs, you should have knowledge about it and only after gaining knowledge will you succeed or else you will fail miserably and will never be able to get up.
Now, the difficult part, Secret to be rich in life. This is very difficult to answer as to be rich in life you have to be content with what you have.
A beggar is happy and feels rich even if he gets to eat only a piece of bread. However a normal person will not be content or happy with only a piece of bread and will not feel rich. Similarly in areas of drought even half a little of water is more precious than money, but is areas where water is abundant people will waste water as they will not know its true value.
Secret to become rich is to be content with what we have and understand the value of things, show gratitude towards life. Money is not everything and will not be able to buy a smile on your face, when you know money's true value.