Here are some things to focus on during the interview...
Always portray a positive demeanor. For example, use a firm handshake, make and maintain good eye contact, smile, and be sure to pay attention to your posture and body language.
Exerting high energy in an interview is important to show interest and engagement in the moment! So don't be sluggish, and have a snack beforehand if you think you'll need it.
Ask permission to pull out your notebook to take notes. Be sure to write down the interviewers names.
If appropriate, ask to share samples of your work or any other supporting documentation that you took along to the interview.
Sell your strengths, but don't oversell, and relate your experience to the job. Be honest about your strengths and skills as they pertain to the position.
Express an interest in learning any skills you may not have listed on the job description that the company is looking for in a candidate. Keep in mind, most employers hire based on potential, passion, and eagerness.
Be sure to provide clear and concise answers. Keep to the questions and topics being discussed. Do not ramble on or veer off on tangents, do not circumvent questions, and be honest.
Get YOUR prepared questions answered and ask any new ones that developed during your interview. An inquisitive interviewee is an interested interviewee.
THINGS TO AVOID
Do not ask questions about other possibilities for positions outside of this interview. For example, if you were to interview for a software development position, you may not want to inquire about product management opportunities. This could demonstrate lack of interest or lack of confidence in the position for which you are interviewing.
Do not be overly opinionated or overcompensate to a point of arrogance. You should support your own style or decisions without criticizing another.
Don't ask "What's in it for me" questions, such as time off, salary/benefits, etc. This will come at a later stage in the process.
In conclusion, be sure to put your best foot forward, as you can only make one first impression. All interviews should be conducted as a means to get an offer. Interviews are time consuming, stressful, and challenging, so why go through all that effort if you do not plan to reap the rewards? Once you receive the offer, you become the one in the driver's seat, and are then free to choose your options.