The simplest thing to get the interview off to a good start, be on time! And being on time really means be early so that you are in the right place and ready to go when you are called for your interview. You really want a few minutes spare to ensure you are calm and composed with your thoughts in order.
Next thing, have your phone switched off. If your phone rings in the middle off the interview might not be the end of the world but it certainly won’t help your case. It’s all about demonstrating that this interview is important to you. If it appears that the interview isn’t important to you then the job presumably isn’t important to you, so why employ you?
Dress to a reasonable standard to at least the level expected if you were in the role you are applying for. If you are applying for a role that really has no dress standard it’s still always better to present yourself in a tidy manner. It amazes me the amount of people that come in with mud dropping off their boots. To me it says you really don’t care or respect anyone else. A first impression will be formed on you very quickly so why not try to make that a positive impression that you can build on while discussing the role and your background etc.