I have read some common "good practices" out there.
Does scrum specify the metrics or the team must determine what and how to use metrics, processes, etc. to the benefit of the product?
The definition of Scrum, maintained by its creators, Ken Schwaber and Jeff Sutherland, is the Scrum Guide.
Scrum goes not require any particular techniques or processes for estimation or prioritization of work. The metrics and techniques used are driven by the environment in which the team is working and what helps the team to succeed.
You could write a whole book answering this question! Happily, Mike Cohen has:
I strongly advise you to try planning poker with your Team. Hopefully you will discover the value of esitmation lies in the process -- the conversations -- and not the output (story points, gummy bears, dog breeds, time granules, etc).
Note to self: need to buy a three-card 1 / TFB / NFC planning poker deck.