Market ALL of your strengths. Employers consider two things: your ability to do a job and your personality. Do not neglect to mention positive personal traits as well as technical expertise.
Give definite answers and specific examples. You will have stronger impact on the employer if you are able to relate specific circumstances to support your answers. Relate stories that indicate your past experience, or explain how you use your skills.
Be ready to talk about your strengths and weaknesses. This is a common interview question. Be honest and forthright - this is not the time to be overly-modest or to pretend that you have no flaws.
Be sure to ask questions in return. Your interviewer will expect it, and it is a good idea to have one or two questions ready before you go in. You can ask about professional development opportunities, reporting structures, the working atmosphere of the office (Casual? Formal?) or the number of people on your potential team. Also, this is a good time to inquire about next steps in the interviewing process, such as when they expect to finalize their hiring decisions, and how they plan to contact each applicant.
Thank the interviewer and shake hands as you leave. Some experts recommend sending a thank you letter the same day. Either way, let the interviewer know that you appreciate their time and consideration of you as a candidate.