You may already have preferences based on your high school experience. Maybe you already know you like hard sciences or don't do so well in languages or have always wanted to write.
Preferences are a good starting point to identify interests.
If you're confused about your interests, try the following resources at Counseling and Career Services. Read the UCSB Catalog . You will see which majors demand more units than others, which have pre-major requirements, review course content, etc. Spend an hour in the UCen Bookstore skimming textbooks required for upper division classes in majors you are considering. In the first week of class each quarter, take advantage of the chaos of students adding and dropping classes and audit one or two meetings of upper division courses in majors you are considering.