The most widely used method is to send the user a link to create their own password.
If however that is impractical (E.G. because you haven't developed this part of the site yet) and still want to invite the user sitting next to you by giving them their first password manually, use a One-Time Secret.
There are lots of services out there, but https://onetimesecret.com is easy to remember.
Don't forget to tell them to notify you if someone else has already read their secret (E.G. The FSB or the NSA has already accessed their account) ;-)
Please click here for the secret you need to access our invite-only service.
If you receive the following warning: #Unknown Secret It
Unknown Secret
It either never existed or has already been viewed.
Please contact us immediately on +00800 IVEBEENHAD