Do your research: Learn about the company and gain an understanding of what kind of operation they're running. This could be as simple as browsing their website and reading through their 'About Us' section.
Ask questions: Nothing says 'disinterested jobseeker' like a lack of questions. You can remedy this by preparing two or three questions you may have. These could be about the role itself (is there any progression available with this role?), about the company (do you have any expansion plans?), or simply about logistics (is there parking or public transport facilities nearby?).
Practice professional hygiene: This is a simple one. Shower, brush your teeth and hair, apply some deodorant, and make sure your hygiene is fresh.
Be prepared for salary discussions: Enter the interview with an idea of what sort of salary range you're looking for. You don't need to prepare an exact figure - a ballpark number should be fine.
Speak clearly: Ensure that you respond to questions and discussions with a clear and confident voice that is free of mumbles.
Be on time: Arrive at least five to ten minutes early. Not only does this give you extra time to prepare yourself mentally, it shows your potential employer that you are punctual.
Look the part: Dress professionally - this could be a suit or shirt and slacks for men, and a shirt with a skirt or trousers for women.
Keep eye contact: Avoid daydreaming and ensure you maintain eye contact with your interviewer. It shows that you are taking the discussion seriously and can maintain a professional discussion.
Smile: Don't be afraid to be friendly and smile. Your future employer will want to see your personality!
Be confident: Show some confidence with a strong introduction of yourself, along with a firm handshake.