Best practice to use OOP

hey guys,

I am still fresh just graduated from graphic design and
I am learning flash + actionscript + xhtml/css/php by my self

I am trying to catchip up with the world with flash
Since, i am learning OOP ffor AS3
what is the best practice for me to use it?
I mean since I am new its always confusing for me
to decided which part comes first and which f function that need comes first

so yeah, tons of advices would be great for me