Everyone is unique. You are unique. Your staff is too. Having consulted hundreds, if not thousands of clients, I know they cannot all be treated alike and given the exact same advices. They each have their own personality and vary on how they deal with people, what they like to address, what they would rather avoid, what kind of practice they prefer and so on.
 
And each of your staff is also their own person with their own preferences, sensitivities, opinions, etc. So how do you deal with them? There are no "one size fits all" approaches. Some people you have to skirt around the issue and compliment them first on everything they do right before you can point out something you would like done differently. And even then, unless you phrase it just right, you are in for half an hour of "explanations" and "excuses" and "reasons" why they did it in the first place. "But I didn't know." "Jenny told me to do it this way." "Nobody ever told me this was wrong." "I have not had training." ...
 
As in any subject, to really be an expert you have to study and drill and intern before you can do. You wouldn't read a little blog on how to do a complex corporate return and jump right in and do one correctly, would you? Yet you deal with your most valuable asset - your staff - regularly, with hardly any training on how to read people, how to predict their behavior, how to talk to them in a way they will be able to accept.
 
And then there is the issue of whether you are actually trying to make a silk purse out of a sow's ear. Some people are untrainable and would never change and shouldn't have been hired in the first place. Trial and error is a very arduous way of learning.
 
My Sterling clients wouldn't dream of hiring someone without a full battery of tests that describes people so well, I've been called a fortune teller, but it's the tests that tell the truth. So you would know whether to spend more time training or use better training techniques or just cut bait. I have had many clients hold on to an employee who was costing them an arm and a leg, not to mention the stress and aggravation, for literally years, hoping the person would all of a sudden change or become productive. Or more likely, hating the idea of replacing them with someone as bad or worse and starting all over again.
 
I also had clients turn away people who, when I made the client call them back into the office, turned out to be the very ones they should hire. So unless you love the thrill of Russian roulette, do not hire people strictly based on how professional and presentable they seem during the interview, or how great their resume looks.
 
But there is one thing that always works with anyone: validating them every time they do something particularly well and ignoring mistakes and imperfections as much as possible. Hubbard says: "You get what you validate," so the more you concentrate on what someone is doing wrongly (that includes spouses and children, by the way), the more they will mess up. But if you keep validating them when they are doing well (the Receptionist who a client just told you how welcoming she sounds, a Staff Accountant who just got a referral, the child who is playing quietly, etc.) - the more of those behaviors you will get.
 
And do not forget to validate yourself every time you do things right!

– Ahuda, Sterling Senior Consultant