Modelling good behaviour
The problem is, that as people, we're not perfect, and we can tell our children to do or not do something, but if we ourselves don't follow those rules, then we can hardly expect them to. How many times have you found yourself telling your children that they mustn't do something, only to then go and do it yourself. Some of these things are big, not wanting your children to smoke when you yourself do for example, but others are tiny little things that you probably don't even realise that you do.
The little things that count
It's often those little things that are the most important. Do you ask your children to keep their sun hats on when outside, and then not wear one yourself? Have you even asked them to be quiet by shouting at them? Told them how disgusting picking their nose is, and then fished around in your own? Non of them are big or possibly even that important, but they are things that we want our children to 'behave' by doing or not doing.
Do as I say, not as I do
Every time you tell your children to do one thing, and then do the exact opposite yourself, you're achieving nothing more than sending a mixed message at best, or showing them that it doesn't actually matter what they say at worst. Do as I say, not as I do? The chances are that they'll just ignore you.
Do as I do
On a day to day basis, you are your child's first and most important teacher. They learn by listening to what you say, watching what you do and then copying. Of course we're non of us perfect, but by trying to make sure that we do what we want them to first, there's a better chance that they'll listen and do what we want them to.