"Write what you know" remains the cardinal rule. Kimmi absolutely nailed it by saying the absolute first thing to play with - and the second - is the setting, with the characters being maybe the third. Change the date, change the location, change the scenarios that bring the characters together, change the characters' backgrounds and internal motivations.
Personally, I've been slower than a lot of writers in changing my voice, even after 90 stories having rarely departed from making (a version of) me the protagonist, always speaking in my own voice. Again, write what you know. This year, I plan to finally enter the Novels genre and write third-person with omniscient narration that can see everyone's internal thoughts and not just my own. But it has taken me years to work myself towards even that. Not saying you would want to take that long in shifting your tone and perspective, but I don't think you need to be in a hurry to do so when there's so much to play with in terms of setting and characters.
Which leads to my other major tip: keep entering Competitions when they come up. You got a great start with Elf on a Shelf. These contests will force you to refine and improve your writing, and to come up with scenarios that would never have come to mind otherwise. Without a competition prompting me to come up with the idea, would I have ever written a 9000-word Noir thriller, or a love story about biking the Great Divide Route that crams six sex scenes and twice as many sex partners into just 2000 words? A humorous, cum-drenched, Hitchcockian piece about solving the mystery of a future genetically-engineered bioterrorist Porkdemic? A tale about skiing and and getting high on pot cookies with former Indian coworkers on an unplanned Christmas layover? Or ... an erotic poem, about anything? Nope. None of these would have come into existence. Sorry if sharing some of the contest entries that I'm particularly proud of comes off as making it about me, but I really, really owe a lot to the competitions I have entered, with or without any recognition for it. It's about the writing, not the winning.