Assuming you are at the casino with the intention of winning and making money as opposed to just playing around and having fun, then going in with the right attitude is absolutely essential. No one wins all of the time, even the professionals have a bad streaks from time to time, so from the very beginning you should not set your expectations too high.
Further, gauge your mood and attitude as you play, if you are frustrated or annoyed, then chances are you will play badly. Similarly, if you are on a great winning streak, keep your happiness moderated as well as over confidence can lose you just as much money as frustration and distraction.
Further it is important to keep your head clear and focused on the game. Perhaps if you are playing slots this is not very important, but it is for any game that requires a degree of decision-making based on the actions of the dealer or the other players. Failing to pay attention, letting your mind wander around aimlessly or letting yourself get drunk are all recipes for disaster.
Though luck certainly plays a role in any casino game, most of them also require prudence and attention on the part of the player. If you are unable to keep yourself focused for whatever reason, you should probably pack it up and stop playing.