Impressions can make or break a relationship with an individual you have just met for the first time in your life. If you don't treat them with the respect they deserve, the person most likely will not like you as an individual. You must be prepared to answer questions about yourself, and to ask questions pertaining to them. Dress appropriately to impress your mentor or boss of the job even when there may be a casual day you can dress. You must seem interested and positive about the job, so the mentor knows you are excited to get started soon on the job. Do not just answer the boss' questions, but ask them questions as well and engage in conversation with the individual who you are trying to impress. Being yourself, looking the person in the eye and sounding confident in your speech is key to a great first impression on the first  meeting with someone.