You only have one chance to make a good first impression. From your clothes, to your body language, everything counts.
When it comes to an interview, you should first be very careful with your clothes. Don´t chose them on the same day, anticipate your outfit the day before so as to dress to impress! Your clothes shouldn´t be too revealing, too tight or too baggy. Also remember that is better to be overdressed than underdressed. Furthermore, keep it simple, don´t over-accessorize and don´t wear too much perfume.
When the time comes, don´t forget to relax. Everyone is human, and the interviewer allows you to be nervous, so don´t let the stress overwhelm you. Shake his hand with a firm grip - without breaking any bones - it will show that you´re confident. Be kind and polite to everyone you meet. You won´t be judged by one person only, the interviewer may ask around him how the people perceived you.
Now that you´re sat, sit up straight on your chair and start with a great introduction. Summarize what you´ve done so far, your results, and what you would like to get out of it. Then, explain why you´re here, and show your knowledge about the company. Avoid using words such as “like” or “hmmmm”, don´t try to fill the air. If you need to think, you can save time by saying “that´s a great question” or “I´m glad that you´re broaching the subject”. Once you´ve said everything, ask question on the job offer to show you´re interest. In case you realize the job doesn´t fit you, don´t stop being polite and show interest and respect to your interlocutor.
When the interviewer makes you understand that it´s finish, smile and thank him/her for receiving you and how nice it was to meet him/her. Don´t forget to mention that you´re available for any further information, and that you´re looking forward to hearing from them. Give another firm hand shake and smile a last time! Now it´s done, take a good breath and be proud of yourself for having given your best!