Well, I try not to use the word no, because my own children threw it back at me. No offence to anyone, but I try to use: 'Don't touch' or 'we don't touch that' or 'we don't do that' or 'we don't say that' or if worse comes to worse 'NO THANK YOU'!
I definitely agree with what Littledragon said about showing affeciotn when they are being good too and I read an article about 'specific praise' which I think is good advice. So don't just say 'good boy' or 'good job', but instead say, 'good boy for putting the toys away' or 'good job for putting on your shoes by yourself'.
Great point on 'specific praise', I also use 'specific correction/cause & effect'. Example "____ please don't climb up on that chair, you will fall down and hurt yourself". For some reason, it's just always been an automatic with me?
Children are great imitators.
So give them something great to imitate.