It's also quite neat to look at other peoples code and steal what you can - there was a good thread on the beta forums where hints were posted. I would have backed it up had their been a warning of its demise *shakes an angry dwarven fist at Turbine*
The thing I have found most useful is a pdf file from the Lua site it can be found on the page http://lua-users.org/wiki/LuaShortReference
and contains the syntax for all major commands - some of which aren't relevant.
I'll give an example; I spent a full day writing code to sort a list. Then, looked at the reference and found table.sort. Oh! How I cried!
EDIT: Off topic, but why don't threads from this forum appear on the front page?