To get this you must earn an S-Rank on every one of the main stages in the game. 9 zones, with 2 acts each, means you need a total of 18. Rival/Boss stages don't count, and neither do Challenge stages. This isn't nearly as difficult as it sounds, as this game is FAR more lenient with S-Ranks than previous Sonic games were.
Basically, all you need to do is get through each stage relatively quickly -- under 6 minutes is generally fast enough -- without dying. You don't need to rush too much, so if there's a section you struggle with, don't be afraid to slow it down a bit to make sure you don't get yourself killed.
Chances are, you'll get a lot of them just playing through the game normally. Not dying is REQUIRED for an S-Rank, but if you die, I recommend you finish the stage anyway if you need to practice. If you've finished the game, you should be able to get most of them within a few tries.
The only stage I personally had trouble with was Rooftop Run Act 1, mostly because of that stupid clock segment near the end of the stage.