i've found that i play poorly -- i.e. calling too much, bluffing in the wrong spots -- when i'm bored and just playing for something to do. there are two ways to play poker: 1) play to make money 2) play for fun. if you're just playing as a way to find something to do, stick with the lowest limits. this will help you avoid major damage to your bankroll and also allow you to try different strategies, although sometimes when you find something useful at a low limit table it doesn't work as well at the higher limits.
if you're serious about making money, you really need to be aware at all times of your mindset and mood. if you start getting bored, quit. you should never be bored with making money. if you lose a pot because of a bad decision, you need to quickly figure out what caused you to make that decision. if you were making a calculated play to take a pot down, that is part of the game and we all know that we can't win them all. however, if you made the play because you were frustrated, or were growing tired of folding rags, then you should quit and not come back to the game for a while. going into the living room for five minutes and then coming back won't help -- you'll just be steamed when you get back in. find something to do that requires some physical exertion, as this helps to clear the mind.