A good answer to the 'What are your strengths?' question would be how you enjoy new challenges and tackle them in an organized manner.
Don't forget to turn off your cell phone.
Do NOT be late. That is an instant fail and you will not get the job. Instead arrive a little early and show that you value their time.
Prepare beforehand and research the company, the people, the culture, etc. Be prepared to match your skills and background to the company's needs.
Don't be afraid to ask your interviewer questions about the company, culture and job position. It shows interest.
Follow up an interview when possible. Express gratitude for their time and continued interest in the position.
Know the answers to tough general questions like 'Describe yourself', 'What are your strong points' beforehand.
Be able to summarize your resume to the interviewer in about 30 seconds in case they haven't had time to prepare for you.
Dress appropriately for the interview based on the job title and wear something you feel confident in.
Think before you speak. Think about what the interviewer most likely wants to hear and tailor your responses to that without seeming fake.