I have a comfortable pair of black knee high boots with 3 inch heels
What are the dos and don’ts of what to wear with them?
I think they’d look pretty hot on their own. But that’s just me. 
Yeah, but that won’t fly at work.
My #1 rule for boots–make sure the top part fits your calves. Boots look bad when the person is swimming in them or the boots are straining to fit.
Other than that, my favorite boots look is to wear them under jeans.
Boots are “in” this year; at least 75% of the women visiting my store are wearing them. It doesn’t seem to matter much what style is going on from the knees up.
Boots are always in, in winter.
For work, it sounds nanny-ish but I’d suggest wearing boots that high with a skirt that covers the knees, and hence the top of the boots. If you can wear above-the-knee at work, I’d suggest, again nanny-like, wearing solid tights to make it a little more professional.
I love boots, and have one pair that comes up to mid-calf, which is not a flattering length on anyone at all, expecially me. 
At least with knee-high it looks good with a variety of lengths of skirts. And of course, if you wear them with a dress, make sure the dress isn’t ‘lighter’ than the boots; keep it a heavy knit or something that matches the season. Otherwise it looks like a bad example of ‘what not to wear’ for most people.
Good advice, especially about matching the weight. I don’t wear skirts shorter than ankle length, but I am looking forward to wearing some a bit shorter with the boots.