The Intelligent Investor by Benjamin Graham
Graham outlines his understanding of markets in layman terms, which consists of these main points:
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.