Have the answer to the almost certain "tell me about yourself question" committed to memory.
For other questions, try to provide examples in your answers. If they say "tell me about your strengths," give them three strengths and then examples that demonstrate those strengths.
Make eye contact.
Research the company and have questions for them prepared. They almost always ask you to ask them questions. I like to say as a default: In the first six months what are you looking for from the candidate that fills this position.
Don't be so nervous. The truth is, interviews aren't that much of a big deal, most are pretty relaxed and aren't high pressure.