There are so many that come to mind that a top 10 list is a bit difficult.
Here is what we do:
An issue of some/any kind comes up.
We create a relatively brief and to the point procedure/policy on how to deal with it.
We ask for a quick review (today) from others at the shop.
We edit it accordingly.
We include it in a weekly email to all staff making it clear that this is how we will do things.
As time goes on, we make adjustments as needed.
Over time we have accumulated well over 100 of these which are specific to our shop.
We have them grouped/indexed for easy reference (oil changes, comebacks, shop care, etc).
We email an updated complete list to employees regularly.
At one time we would try to create policies and procedures in advance, however we found that for most issues the result came out better if handled right when it came up.