A critical point to remember while practicing, is to avoid memorizing what you want to say. Whether you are talking about yourself or the company with which you are interviewing, let it be a natural flow of words. If you come across like you have a speech prepared, your interview will be less effective. You probably will be nervous during the interview. Concentrate on what is being asked and respond appropriately.
Many people make their voices more monotone to sound professional.
Use normal tone and don't speak too softly. It is better to be a few minutes early than one minute late for your interview. Interviewers have a busy schedule and if you are late, it will cut down the amount of time allotted to you. Most important, if you are late you will make a bad impression. If you are seeking a professional position, you must look like a professional.