If this is the first time you are going to face an online interview you need to practice a few times before diving in the actual scene. In the initial takes, you are bound to make some mistakes which will eventually be sorted out as you practice more.
You can ask a friend to speak from the other end of the screen and take a mock interview.
What if the laptop shuts down in the middle of the process? Or the audio system is just not good enough to function properly? You cannot afford to offend the panel due to these silly reasons, can you? So prior to your interview get all the technical stuffs checked by an expert.
You need to have a good internet connection if you want the interview to run uninterruptedly. A fast internet connection is the most important criteria of an online interview.
If you do not have a sound net connection in your home you can borrow a 4G wireless modem from a friend or arrange the interview in a friend’s place who has a broadband connection.
Just because you are participating in the interview from comfort of your bed room doesn’t mean you should sit in front of the screen in your linking park tees and shorts. Dress in the same way, how you would have dressed in an offline interview.
Please keep in mind that whatever sound you create near the system gets magnified and reaches the other end with greater intensity. So do not move much during the interview and avoid handling objects (like scribbling with a pen, checking your mobile, turning pages etc) near the system. And yes, keep your phone on silent (not even in vibration) mode and turn off notifications on your computer.
It often happens that the microphone delays the transmission of audio due to a number of factors (primarily slow net connection). So make sure not to speak at 100miles an hour. Go slow and steady.
It is important to make eye contact throughout the interview. For this, avoid looking in the screen randomly and try to look directly at the webcam.
Prepare your subjects in the same way you would have done in case of an offline interview. Speak confidently to show your command and confidence in the subjects.
Presentation is very important in all aspects of life. Take care not to have objectionable objects or images around you or in the background that can send a negative signal to the interviewer.
Keep all your documents, certificates and other useful items near your desk. It makes no sense to search for a pen and pad in the middle of the interview process keeping the interviewer on hold.
Know your would-be organisation: gather all the important details about the organisation you are going to join if selected.
Finally do not show symptoms of nervousness or stress during the interview. Practice a few rounds of deep breathing prior to the interview and keep a smile throughout the process.