What sort of things do you say?
What do you not say?
I find that when dd does something and I want to let her know I don't want her to do that, the right words don't come easily.
Dd is 22 months old, so am talking about behaviour such as pushing her friends over or refusing to share her toys. I don't think either of those things are 'naughty' at that age, and I don't go for punishment or being cross, but I do want to let her know that it's better not to push / hit / snatch etc.