There is no one best practice I'm aware of. Here are some links:
- http://web.elctech.com/?p=79
- http://reinh.com/blog/2009/03/02/a-git-workflow-for-agile-teams.html#production-tagging
Generally, versioning (0.0.1, v0.2.1, ...) maybe hand in hand with some issue-tracking could be considered a plausible approach. (.. although I usually use v-prefixed tag names .. see also @VonC answer)
