Saurons Plan

I am reading "The Simarillion" at the moment and a question has come to my mind.
What was the plan of Sauron? If he had conquered and gain rule over all the lands of Middle Earth? Conquer farther? As far as I know there is no hind or something what really was going on in that evil mind. But maybe some of you know an answer, or at least a suggestion.
I myself believe that if he had succeded he would have tried to free Morgoth from the void. It must be possible?

Thanks for your answers and deeper insights...