I highly recommend reading Reminiscences of a Stock Operator

These are some of my favorite quotes from Reminiscences of a Stock Operator by Jesse Livermore/Edwin Lefevre:

On cutting losses and letting winners run:

In speculation when the market goes against you- you hope that every day will be the last day and you lose more than you should had you not listened to hope-to the same ally that is so potent a success-bringer to empire builders and pioneers, big and little. And when the market goes your way you become fearful that the next day will take away your profit, and you get out too soon. Fear keeps you from making as much money as you ought to. The successful trader has to fight these two deep-seated instincts. He has to reverse what you might call his natural impulses. Instead of hoping he must fear; instead of fearing he must hope. He must fear that his loss may develop into a much bigger loss, and hope that his profit may become a big profit.

How to tell when the stock market has topped:

A market can and does often cease to be a bull market long before prices generally begin to break. My long expected warning came to me when I noticed that, one after another, those stocks which had been the leaders of the market reacted several points from the top and for the first time in many months-did not come back.

On bear raiding:

The public ought to grasp firmly this one point: That the real reason for a protracted decline is never bear raiding. When a stock keeps on going down you can bet there is something wrong with it, either with the market for it or with the company. If the decline were unjustified the stock would soon sell below its real value and that would bring in buying that would check the decline. As a matter of fact, the only time a bear can make big money selling a stock is when that stock is too high. And you can gamble your last cent on the certainty that insiders will not proclaim that fact to the world.

On rumors:

The public should beware of explanations that explain only what unnamed insiders wish the public to believe.

Naturally, promoters, manipulators and other beneficiaries of anonymous optimism will tell you that anyone who trades on rumors and unsigned statements has only himself to blame for his losses. One might as well argue that any one who is silly enough to be a drug addict is not entitled to protection.

The nature of the game as it is played is such that the public should realise that the truth cannot be told by the few who know.

On trading day in and day out:

I have said many times and cannot say it too often that the experience of years as a stock operator has convinced me that no man can consistently and continuously beat the stock market though he may make money in individual stocks on certain occasions. No matter how experienced a trader is the possibility of his making losing plays is always present because speculation cannot be made 100 per cent safe.