Hey! I really love Lua. I'd recommend reading Programming in Lua (whatever the latest edition is) and Lua Programming Gems. Unfortunately, Lua is one of those languages that isn't written about a lot because its use case is usually for embedding. You'll have to do some legwork to read how other people write Lua. You probably want to read a lot of code on Github. Olivine Labs springs to mind here as an org that uses Lua quite a bit, but there are more. I got off the Lua train at 5.1, but 5.3 adds a lot of niceties.

Depending on how deep into the rabbit hole you want to go, reading the VM source code is instructive too (it's a pleasant read at ~10kloc. I'd actually recommend reading it on the website as they've hyperlinked much of the code.)