Smile... enjoy yourself on the court. Are you only in a good mood if you're playing well..? But what are the chances you'd play well if you were in a really good mood...? Maybe a better question is how often do you play well when you're in a really bad mood...? Maybe the correlation works both ways.
How you move influences how you feel, but how you feel also influences how you move. Keep that in mind... you can't necessarily control how you play on a given day, but you can control your attitude.