As clutteredup suggests, look over whatever documentation you have from them (e.g. job advert, person specification and job description) and work out what sort of skills, experience, qualifications and personal qualities they are after. Even if you only have a job advert to go on, the main criteria will be there. Then you can write a list of likely questions and think about how you can respond, wherever possible giving practical examples to persuade them that you have the relevant attributes.
You should be able to pick up lots of information on their website, and it's worth doing a general search for any relevant news items about the organisation. Think of questions to ask them based on your research.
When you are being interviewed, try and spread eye contact across the panel, so that you're engaging with all the interviewers.
I often think that enthusiasm and a positive attitude are so important in interviews and at work - if certain skills/experience are classed as 'desirable' rather than 'essential' for the job, enthusiasm and attitude can go a long way in persuading an employer that you have the ability to acquire them.
As GrendelsMum says, practise your presentation thoroughly so that it will be very familiar and natural when you come to deliver it.
Good luck for Friday. You can only do your best and even if you don't get the job, it's all good experience, so try not to get stressed about the process, and enjoy it if you can!