When you watch other comedians, notice how they define themselves. Look at the acts that are truly unique, and others whose material is interchangeable, could be done by anyone, and doesn't reflect a unique point of view.

Then look at your own material and consider the same thing. In the beginning, it's okay if others could easily do some of your jokes. That's only natural. But start looking for glimpses of your personality shining through in certain jokes, and start cultivating that type of material. Look for ways to expand those special jokes, and weed out the generic stuff or adapt it to fit your personality a little better.