Here you have a couple of style guides related to ruby, rails, and some tips on functional programming and a few not-so-trivial techniques like currying, TCO, or just using immutable structures.
Apparently, all things explained in all those guides are obvious, or just a matter of taste, but you better read those guides a few times each to make those rules stick in your head, just to be sure :)
First, a guide from bbastov (of emacs prelude fame), that's already in github and forked more than a hundred times, so we could say it's a community ruby style guide.
Second, another bbastov's guide, this time on Rails 3.
And last but not least, slides of a friend of a friend's workshop on Functional Ruby. Really nice, and full of nice tricks that deserve to be read and understood.
That's all for now. Back to hacking