It is possible for a management layer to be wedged into a business unit that is already performing well
but the manager(s) involved will find that some approaches do not work. A huge danger is that 
The performance of the unit will fall on your watch. I have drawn these ideas from personal observation
of a company I don't work at but have met the owners, management and employees. 

To the owners: 
It may be possible to promote some employees to a supervisor position without all the stress and trials of a new management layer.

To the middle manager: 
The most important function is to handle the communication that used to go to your boss. You must 
intercept the old communication channels without negative methods. Assume your authority to be respected, don't be surprised if it is not.
Expect to earn the respect for your position.

Be consistent in your reactions to the infractions. Be proactive in learning the processes of the production.

Micro-management, threats, abusive environment, power games, browbeating  and negative feedback all effect moral. Why do you care? 
Good moral  = productivity, bad moral = problems, conflict, lower productivity, your job lost. Know to delegate authority, 
since the unit was already running, it will become obvious which people to hand the ball to, they already have it. 

Workers will resent you because:

    1) They already know how to do the job.
    2) They will have to train you, then you boss them
    3) You cannot do any part of their jobs.

Answers:
    1) Respect them for that 
    2) Put the spin on, have them show you what they do so well, don't flout your authority
    3) Pick a task you can learn and do it when normal scheduling falls short.

Do learn an employee task, how can you manage them without knowing what they do?
Do not be overly literal when applying workplace documentation, it may be flawed. 
KNOW THE PROCESS FIRST, learn the existing systems. 

Avoid punishment over trivial infractions that may be part of the employee accepted
workplace perks. Do not ignore them or make threats, small costs can be used as rewards. 
The large cost is the lost productivity from resentment. 

Occasionally the infraction is not trivial, Know the review and firing process.
Do NOT threaten to fire people unless you are willing to carry through.

Do NOT try to justify your position by nit picking over the employee's practices.
Negative feedback will NOT work and may never work

Do NOT change things without a clearly defined reason, it will be seen as
A justification of your existence The energy and effort wasted.

A rigid structure applied to a flexible environment will consume resources as attempts are made to make it fit.
Every time the flex occurs, the structure will require duct-tape. If the basis for the structure is management comfort, productivity will suffer. 
For example, In this flexible workspace, workstations can move and often do as the changing nature of production requires. 
To facilitate micro management, a map of the workstations was made. This flies in the face of established procedures that depend on flexibility. 
The map has a limited lifespan.

Do NOT assume you are always correct, you may have missed a vital piece of information
You will be remembered for that failure.

Do NOT tell the employees that you have no intention on making friends, 
it may be true but telling them that gains you nothing.

Do expect the employees to go over your head, remember, they don't need you.
The people that hired you need you.

Do NOT lay down the rules in a employee meeting and then break them yourself, it is the old
'Do as I say not as I do' syndrome, which gains you contempt.

Do NOT be a negative manager, avoid lists of 'bad' things, it will get negative results.

Do expect to work, give praise and be fair,  they will pull with you, not against you.