Princeton’s Burton Malkiel looks at many of the theories of investing and some ” Stupid investor Tricks ” as well.
He concludes that the cheapest, most successful, lowest-taxed route for many investors is in an index mutual fund ( the Wilshire 5000, the Russell 3000 ) for at least the core of any investing strategy. This the ninth edition (2007) is fairly easy to read and yet comprehensive.
Investing seems to get less scary the more you learn about it. This book is a pretty good start.