Lots of great in-game tips out there such as how to play your cards or how to control your emotions; however, none of this matters if you aren't disciplined in a few areas outside of the game too. Bankroll management is a perfect example of that. Your poker skill might rival that of a seasoned pro, but if you're risking too much money in events regularly (or worse yet, don't even have a bankroll plan), then it is only a matter of time before you go broke. Variance is no joke and it just takes one or two close downswings to put you (quite literally) out of business.
Having a solid and disciplined bankroll/bankroll management is essential. How much is a "safe" bankroll? It depends on many factors. Not only the stakes of the games, but also your edge over opponents and also your willingness to lose your bankroll. You should have a much larger "safety net" if this is your only money for poker versus someone who can easily reload money.
Chris Ferguson recommends putting no more than 1% of his bankroll at risk per game/session/event.
Closely related to bankroll management is table selection. You want to win more often? Play worse players! It really is that simple. Find a game you can beat consistently, put in the volume of games and simply "print money." If you are more interested in improving your poker skills, then by all means seek out challenging competition, but understand that you probably won't win nearly as often as you would against "softer" competition. What typically off-sets this enough is if the higher stakes games are profitable for you and the "soft" competition only plays much lower stakes. In this event, then playing the tougher players might be better if you are willing to drop back down in stakes (to the softer competition again) if you begin losing and need to build your bankroll back up.