A lot of writers come back to the same themes again and again, from father issues to aliens, most writers seem to have their private preoccupation. The problem with this is that you want to have work that sounds different, that explores new themes and interesting topics.
For a long time every piece of writing I worked on had the word lull in it, I also liked writing about dusk, and metronomes. Now most of those words are gone from my work, even though I am still writing about the same topic.
One of my students said he can never write a story without starting with a character waking up, another said that she somehow manages to kill a character a chapter if she doesn’t stop herself.
One of the easiest ways to try and write about new things is to make it clear what you normally write about. Some people are not even aware of their themes or tendencies in their work.
For this exercise you are to write down all the themes and words that you feel like you use most often.
Then you have to come up with a theme or a plot, or a setting that has nothing in common with what you normally write about. Write for fifteen minutes.
After you are finished, review your work while looking at the list of themes and words that you tend to use. If you managed to use of those words or veer into one of those themes, either cut that part out or start over again.
Even if you never write about this new setting or theme again you have stretched your writing muscles in a new way.