How to stop constant complaining (9 yo) and not listening?

[runningandjumping]

My 9yo son is constantly complaining and even getting angry about doing even the most basic things like taking a shower or cleaning his shoes, putting his dirty clothes away etc. Also he has a tendency not to follow the rules when I'm not looking (e.g. I just found out that he didn't brush his teeth for several days in a row - he was just pretending to go to the bathroom and do it and I only found out because I found his toothbrush in another bathroom)/ He's a very bright boy, doing well in school, he's kind to his 2 siblings, and is generally sensible.
My question is - how do you encourage positive behaviour and stop complaining and not complying with the rules?

Praise the good things.

Tell him how, now that he's older, that you can trust him to make the right choices.

Stick and carrot rewards; pocket money.

For just 10 minutes listen...really listen...without interruption or judgement to what is really upsetting him, then do what you can to help him see that some things he can change and others he will just have to accept and stop wasting angry energy on.
Keep telling him you love him but you find his actions hard to accept and confusing. (though this behaviour isn't untypical of a boy his age; he'll change when a special girl comes onto the scene)

sounds like a tough one...I would definitely try to talk about what's going on. From what you've described he is a good kid - so worth a try to ask what's happening! Hope you can get some answers...