If one of my friends is going to have an essential job interview and wants some suggestions, I would say two things to him. First, dress properly and second, be yourself. Since this is a formal occasion, it is better to wear professional clothes, like wearing a suit or a tie. This way, he could leave a good impression on the interviewer and share a greater chance of successful employment. Speaking of being yourself, it just means take the interview as a casual talk and communicate your ideas about your own expertise. Sometimes pretending you know something that you actually don’t know can hurt you in some way. So if you want the job, just be honest and be yourself. And these are the two suggestions I may give to my friend.