I hire people all the time and a few things will help you get in the door.
Resume homework, do homework on the job and detail it in the resume. If your want to work at a guitar shop explain your ability to play, food.. know the menu, your knowledge of the product and tell about your customer service skill and that you love to help people.
Dress for the job, come in with clean gear and not a Slayer shirt, not geeky but a plain button up shirt and jeans NOT OFF YOUR ASS!!!!!
Say hello Sir Miss thank you for taking the time to see me, if its a hand shake squeeze like a nice ass...ok like a nice orange not hard not soft.
Is there is anything else I may be able to add to get this job?
Say it with respect and leave it hanging.
Thank you for seeing me, would it be alright if I call you in a few days?
Trust me, lots of people don't have a clue for even a small part of the above. Do your homework and know everything thing about that company and tell them that in a nice way... E.G. I see you have the new JP7 in the BFR series, great guitar for $$, I see you have steak on the menu with 3 sides, most have only two..