I'd announce myself globally, punk out a wide array of fanatics, terrorists, and tyrants in ways that would evoke as much laughter as they would righteous fist pumps, and then I'd set to work helping humanity in more subtle ways. Y'know, help them crack various secrets of the universe, how the human body works, how to make some really bitching cool artificial intelligence, that sort of thing. I'd go to all sorts of geeky shit, conventions and what not, because if God was giving it the thumbs up, hey, kinda out of vogue to NOT be into it at that stage. I'd make a bitching awesome headquarters somewhere, like maybe Egypt or Texas, that would look like the fever dream acid trip creation of H.P. Lovecraft and Tolkien combined. And once a year I'd bring back legends of humanity's past, from historical leaders to kick-ass musicians, for a week long history festival that would culminate with unfairly awesome concerts.
Then, one day, once I've more or less confirmed myself as one of the coolest deities outside of fiction, I'd call a press conference- because, yeah, could make myself manifest to everyone simultaneously, but that's so rude and invasive -and point up to the stars.
"Humanity's destiny is out there. Time to start finding it, folks."
And just because I can... I'd have Lucas design humanity's first capital starship. And then just jury-rig reality to make it work. Though if he mentions Ewoks or Gungans, I'mma have to divine slap him.
Oh, and once a decade, I'd just make it rain Pop Rocks on a major metropolitan city. I would never explain this action nor even directly admit I was doing it.