If I'm taking over the role of the Abrahamic God, first thing I do is put a world of hurt on anyone who's acting in MY name. Sarah Palin, Benjamin Netanyahu, and Mahmoud Ahmadinejad alike would all have severe anal bleeding and stigmata to let the rest of the churchies know there's a new God in town and he's PISSED.
If I'm just becoming a god in general and have to build up my worshipper base from scratch? I find the nicest, most morally sound person I can and start showing up in visions. Then if the psychiatrists start pestering him for preaching, I show up and give THEM visions that make them doubt their own sanity so eventually people put two and two together that yes, this guy's been visited by a real god and that real god would rather the religion founded in his name be a kind, caring, decent one that draws followers by example (and a bit of divine intervention when the god in question gets bored.)
Or I go Sheogorath on all humanity like that Daedric quest in Oblivion and make my afterlife as much like the Shivering Isles as I can decently get away with. Then I start messing with Todd Howard's head until he's gripped by a singular obsession to make Elder Scrolls games and DLC until he breathes his last. Someone else (like JE Sawyer) can make Fallout, but Mr. Howard? You're on a mission from God.