A simple but very important stock market for dummies rules, always follow the rules.  This is a very basic yet important one because this helps you to discipline yourself. You should condition yourself to follow the established rules. Easier said than done because of our human side that tends to modify or break the rules and find some reasons for doing so.  For instance, we might see a stock that is doing very well and have the tendency to jump in it hoping that the run will continue.  Of course this is breaking a rule in that you should never jump in a stock run late.