[Zyonin]

I don't know about guides to efficient Lua code, however if you have an IRC client (they are easy to find and you may have one without even knowing it), then go over to:

irc.freenode.net

and join the channel:

#wowace

Then you can talk code with the various crazies over at WoWAce. Otherwise find some good examples of efficient code (Tekkub's mods are a good example, then again I am just a novice coder myself), take em apart and see how the author has put it together.

Another IRC channel is:

irc://irc.freenode.net/WoWUIDev