I have learned in life that whenever I need something from somebody, it helps grease the wheels of whatever we're talking about by making it easy for them, while also trying to make the entire experience at the very least satisfying for them and that I truly appreciate the effort. I'm not talking patronizing them. I'm talking respecting them while treating them as a person and not a nameless minion.
Please and thank you goes a long way towards that. Tone of voice goes a long way too - never vent your mood on them.
For example, in checkout lines I always try to make the checkout person laugh or smile if possible (you gotta think fast and be able to read their mood quickly to know what to hit them with) - but at the very least make the experience for them as painless as possible.
Having your debit card ready to go, knowing the prices of what you bought so you're not sticker shocked, no cell phone in the line ever...those types of things. I read name tags so when they say hello, I reply (for example) "hello, Carol".
I'm never, ever "THAT guy".
I do this everywhere I go, whomever I deal with, no matter the setting. I treat them like a person wants to be treated. It's not hard to do at all, it costs me zero effort and zero extra time. I simply try to give them that one moment a day that makes their entire day of drudgery worthwhile by employing the simplest of respect towards them.
I tend to do much of my grocery shopping and my prescriptions at the same store. Have for years, usually at the same times of the day. A menagerie of employees come and go. BUSY place, probably 2,000+ customers daily are in that store (probably being way too conservative on that estimate). But I do, in the maybe 40 times a year I'm there, run into the same employees over time.
Some of the people there actually know my name. One gal, who has been there for about 5 years and is now a manager, will see me there, stop what she's doing, and chat me up for a minute with a big ol' smile. All from those 3-4 times over a couple years when she was my checker where I treated her nicely.
I'm in that grocery store maybe tops 10 minutes each time, and interact with the employees maybe absolutely tops one minute each time. I get a repeat employee maybe at most 4-5 times a year. And a few of them actually know my name out of the tens of thousands of nameless faceless customers that walk through that door that they encounter.
Can't remember the last time I've gotten a "no problem" in return...anywhere. Convenience/hardware/grocery stores, restaurants, doctor's offices...doesn't matter.
