I find that the best book if you want a deep understanding of the language is Odersky's Programming in Scala. Complete, thorough, well written. It does expect you to have some programming experience, and some bits are perhaps over-detailed, but as long as you allow yourself to skip the bits that bore you, you're in for a treat.
A few years ago I joined a group which had been using scala for a while (since '09ish IIRC) and I took the coursera class to get up to speed. It definitely helped but the reality was that their code base was closer to being java++ than to haskell and a lot of the early habits I picked up from the coursera class were immediately beaten out of me once I got rolling there.
One could argue that they were in the wrong, but I disagree - Scala is a multi-paradigm language and not everyone is going the FP route (I recently heard Venners refer to Scala as a "reform movement for OO, which is how I personally treat it, but that's neither here nor there).
All this said, I don't have a better suggestion. As I mentioned I took the Coursera class and read the Staircase book. The Twitter stuff online was useful but mainly I just read as much as I could online, tracked down conference videos, etc.