I've gone ahead and tagged this as a draft. I don't have time right now to look it over in detail, but I see several things that I wouldn't necessarily characterize as "best practices" and it may be that this doesn't belong as a subpage of Extension:Scribunto at all.
Topic on Help talk:Lua/Lua best practice
This is pretty well known good practices, and yes I do know that it goes against some of the coding done in Lua code for Scribunto.
I was wondering how long it would be before someone complained, and if I should put in references, but I sort of hoped the best practices was so obvious that no one would complain.
I guess it could be posted as a separate help page. Would perhaps be better so to avoid the "my baby" problem.