The advantage of coming into management from the shop floor was that I could do the jobs of people under me better than they could. In some cases I taught them how to do their jobs in the first place. After I became a manager we introduced a new system where people in the sales office directly involved with other areas of the company spent a week working in those places finding out for themselves the everyday problems they were faced with. This was also done in reverse & worked very well.
That's a great idea. I know a certain company that could stand to try something like that... I often wonder if some of our "sales engineers" and design engineers have ever worked in the field

... a big part of my job is correcting their boo-boos. Then there's the (outside) consultants and programmers- groan...

I agree. This is probably THE most important thing. Courtesy costs nothing & can make all the difference to working relationships. I always made a point of asking people to do things for me, not ordering them about. I also made it clear that if anyone was unsure of anything not to be afraid of asking me instead of trying to be clever & inevitably mess the whole thing up.
I'll add my "harrumph" to that- very important points. I really hate the obsequious, treacly request (usually just an act), but it's amazing how different a directive can be when presented with that little bit of respect. And "thank you" is a big one in my book, whether I'm giving or receiving... of course, nothing says "thank you" like money

. Maybe I'm just greedy, but after 5 years of service I was hoping for more than a paperweight, a "certificate of appreciation", and $200... more than many get, but my peers with other companies get a bigger bonus every year. I know... "go someplace else, then"... I'm working on it!
And especially when I'm confronted with a crew of union electricians who've never done any soldering or crimping (uh-oh), I'll follow my crash course with a heartfelt plea to speak up if something doesn't make sense to them. I find I have to bite my tongue when somebody doesn't get it after repeated explanations, too- they'll just get pouty and get less done, and bottom line is that if they aren't learning whatever, I've failed to teach it properly. There's a limit of course, but usually there's someone with their local to whom I can turn and request that they be reassigned or whatever, if it comes to that.
Respect and humility have to be there to temper authority...