The Intelligent Investor by Benjamin Graham

Graham outlines his understanding of markets in layman terms, which consists of these main points:

1. The market appears irrational
2. Buy when the depressed market offers things at less than their value
3. Sell when the exuberant market buys things for more than their value
4. Develop a quantitative model for valuing things

Graham revolutionized the analysis of companies with his Security Analysis in 1934, popularizing the quantitative analysis of companies as money machines. Naturally, developing and testing models seems like a good next step for an interested investor. However, I've not yet found a good introduction to modelling, the best so far lies in an integrated statistics approach via DataAnalysisForPoliticsAndPolicy.