My first post here :)
I can't make tutorials because I'm still learning with the help of your wonderful tuts, but I hope this can be useful for other newbies like me.
In
Wikipedia there's a simple and very good explanation of what the rule of thirds is and how to use it.
I made a very very simple 100x100 square divided into thirds and highlighted the diagonals too, to use as a guide in the icon making process.
the psd is
here