Try to be working as much as possible. Don’t lean on anything, and for the love of Fluther don’t sit down unless you’re on break.
A history of customer service suggests that you’re good at people. Crank up the charm and leave it there for the duration of your shift. I’ve found that keeping your eyebrows partially raised is a low-effort way to appear friendlier.
Go in with a good attitude. Even if you have to strap it to your face and call it persona, a good attitude is paramount.
Demonstrate a willingness to help. Stay late when they ask, come in early when they ask, cover shifts when they ask. Do things that you can do before you are asked to do them.
Don’t complain about anything, not the people, not the boss, not the pay, not the hours, not the co-workers, not even the lousy washing machine.
If you mess up, ‘fess up. If the situation calls for it, of course. You can probably handle a mop as well as the next guy, so spills are probably out.
Incidentally, it helps to know how to mop a floor.