For many artists the path to defining a style is long and treacherous. It takes so much exploration and evaluation to figure how you want to create, what you want to create, and how you express yourself. It really can be painful at times, but it's so rewarding once you finally find a direction. However, this process can leave you feeling afraid to explore for fear of getting lost or diluting your brand.
As artists it is important for us to never lose that spirit of exploration, but in exploring we have to be cautious about what we share and how these explorations are affecting our work. Sometimes exploring is as simple as applying our work to a new medium. For example, Andrew Maclean is primarily known as a comic artist, but he has just started making patches.
Many artist explore specific themes and content in their work. A lot of this simply comes from what they are interested in. Personally, I find myself drawing characters from movies, musicians, and comic characters. I draw these things because I love them, but to be marketable as an illustrator it is really important to work outside your comfort zone. Exploring new subject matter is a great way to explore and demonstrate marketability.
Sometimes you get the push you need from a client. Last week I was hired to design a poster for the wordpress mascot Wapuu's fanclub. Cute anime mascots are not something that I would have ever considered drawing, but the project had just the right level of challenge to really inspire me. I did a fair amount of research but just the idea of applying my style to something that I normally wouldn't draw created an interesting juxtaposition that made this project a lot of fun.