Hi Simon,
What sorts of best practices are you looking for? We support a few different variants on external sharing, depending on what types of scenarios you are trying to fulfill.
Our most frictionless experience is to get an anonymous/shareable link to the item. This works exactly like an email attachment, giving the recipient the ability to open the doc without sign-in.
We also offer sharing to specific people which requires the user to prove their identity via sign in with Office 365, a Microsoft account or with an email verification code.
Finally, for longer projects, you can add an external user to an Office 365 group where they get access to all of the group's resources.
I highly recommend tuning into Eugene Lin's sharing talk at Ignite 2017 tomorrow for a deeper look at all of this.
Hope that helps!
Stephen Rice
OneDrive Program Manager II
