It sounds like you've found your comfort zone. While that can be a useful place to linger and explore, it's often a good idea to launch yourself out of it in order to continue growing and developing as a writer. Below, you'll find some exercises you might try to make this experiment seem less daunting.
Character questionnaire: Sometimes writers are stumped because they simply don't know where to start. Consider creating a list of questions you might ask about a character and then fill it out, keeping in mind you're working toward a character unlike yourself. Start with a difference that is basic—give the character a different gender, cultural background, living environment or age—and work from there. If you're not inspired by the idea of creating your own list, check out the lists at Gotham Writers Workshop's website.
Make a connection: Brainstorm a list of 10-15 personality traits that are very different than your own. Choose three that you'd like to incorporate into a character. Begin freewriting on that character. Put the character in a particular place at a specific moment in time and let the action unfold. Don't put any pressure on yourself to start writing a story. Just focus on developing the character. When you get stuck, consider a connection that exists between yourself and this character. Draw on the pool of emotions that we all share as human beings. Has your character gone through a divorce? That circumstance involves a loss. What losses have you experienced in your own life? Begin freewriting on about your character again, focusing on the emotion you experienced during your loss. Remember, the situation doesn't have to be similar in order for the emotion that underlies it to be resonant.
Fieldwork or research: Choose an occupation, hobby or practice that intrigues you but that you are not already involved in. Research that topic. You might do this through books, articles in magazines, or by reaching out to someone who engages in the activity and talking to that person. Begin to build a character around what you learn as a result of your exploration.
Collaboration: Work with another writer to create a character. You might alternate writing a passage, switching every three or four sentences. Even while staying true to what you've written, you're bound to find your writing partner will take the characterization in directions you don't expect. While you may or may not develop a story based on this character, it could be a freeing experience to transition out of your comfort zone and into new territory.
As you begin to develop a character unlike yourself, make sure you check in from time to time. Some writers will wrench a character back to the comfort zone without even realizing it. If you find this happening, make a list of the similarities and respond with “what if?" questions that force you away from autobiography. What if the character were a skydiver instead of a runner? What if she worked with dogs who pulled sleds instead of training seeing eye dogs? What if she were dissatisfied with her relationship with her mother instead of quick to find refuge in it? This will help you stay focused—and outside your comfort zone.