There are many factors involved in writing a hit.
But one of them is to have an exciting chord progression.
And if you ever tried to write a song you'll know that finding exciting great sounding chords out of the useal can be a hard task.
If you have an iPhone or an iPod Touch You'll can use an app called ProChords that instantly can show you what chord can be played next
but if you don't you'll have to go the hard way and go through the different chods one by one to find the ones that matches your needs
I have made a script that shows all the close related chords - you can hear how they sound and see how they are played on the piano.