Firm handshake upon meeting them. Look them in the eye and say hello. Smile. Show respectful confidence.
Yes sir/ma'am. No sir/ma'am.
Your qualities: You are a hard worker and a team player. You also work well (heck, even thrive) in fast-paced environments. This is important to bring up since you will be working retail over Christmas (may Jeebus have mercy on your soul). You are well organized and have great attention to detail.
If they throw that "are there any negative qualities you have?" shyt at you, hit them with the "Sometimes I am too organized/too thorough/too hard on myself to do a good job" Hadoken-ether.
If they ask if you have any questions for them, ask them what a typical day's duties will be. Ask how large of a team you will be working with on your specific tasks. Ask who your supervisor will be, and if things are going well, ask to say hello to him/her before you leave - "Who will my direct supervisor be, should I be hired? Would I be able to introduce myself before we finish?"
Ditto to the be on time. This is crucial. Be 15 mins early actually.
Don't need to dress in a suit for a target interview, but nice slacks (do the kids still say "slacks"?), button-down shirt and casual shoes.
Godspeed.