The book Warren Buffett has recommended the most is "The Intelligent Investor" by Ben Graham.

Here are some timeless principles from the book that you can use to invest better:

1 There is a difference between an investor and a speculator.
A speculator looks at prices.
An investor understands that a business is a living, breathing entity and not just a number.

2 An intelligent person might not be an intelligent investor.
The right temperament makes a bigger difference than IQ points.

3 Just because a business grows, it does not mean your investment will grow at the same pace.
The airlines industry in its early years was a great example of this.