A few semesters ago I was taking a TV Script/Screenwriting course at UCF. While the format for script and screen writing is completely different than the writing I have been focusing on in the Writing for Publication course, we constantly experimented with different writing exercised to help establish what works best for us as writers.
Many of the students in my script/screenwriting course realized how imagery and details were there strong points, whereas I learned dialogue is something I write well. We would take class time to write in non-script form and find out strengths. It was afterwards that we would learn how to change it to what format we needed.
I think this type of experimenting with exercises that move one out of the comfort zone and even the type of writing that is not designed for what you are trying to write for can help writers explore the strengths and weaknesses. By moving out of our medium as a writer we can clearly identify what our style really is.
Some of my favorite exercises that might help define you as a writer include:
Write a short story using the first sentence from a newspaper or article.
Write a story with two or more characters and no dialogue.
Rewrite a previous work without any adverbs.
I think many of us still in writing courses tend to primarily write for school versus ourselves. If we want to improve and become more distinct, we need to challenge ourselves, even when we write for our own enjoyment. If we take the time to perform these types of individual exercises we can feel more confident in our work and our style.