Offering a tangible story or example that highlights your skills usually goes much further in an interview than simply telling your interviewer you're good at something. (i.e.: Telling a story about a time you tracked down a tricky bug versus simply saying "I'm good at problem-solving!").
Review the STAR method, discussed in this lesson on non-technical interviews. Use the STAR method to practice answering non-technical questions with your partner.
Again, if you come up with a story or example you feel good about, jot it down somewhere! It's tough to come up with stories like this in an interview on the spot. Having a few tucked away to review before an interview will be a huge benefit to you later.