I read through Scala for the Impatient when I was initially learning Scala a few years ago. It's relatively new and written for version 2.10. Scala is on 2.11, but compared to 2.09 → 2.10, the changes are minimal. The book itself cuts out a lot of the BS and gets down to what a user wants to know about the language (features, syntax, how it differs from Java, etc).
Most Scala books were written pre 2.10, which makes them outdated enough that it would be hard for many new adopters of the language to get much out of them.
First 1/3 of the book is free online. The entire book is only $20 or so on Amazon.
With so many features, and so many of them built mainly for library developers, learning the language by yourself can be very daunting. I wonder where I'd be if I had not done a whole lot of the learning from reading a lot of idiomatic code written by well known developers. It's way too easy to end up writing Java with functions, or falling into common pitfalls that make code very hard to maintain in the long run.
If you've done the first Odersky course in coursera, the one he does with Roland Kuhn and Erik Meier is a very natural progression that will be far more practical than the original.
There are good series of blogs out there that, although somewhat outdated at times, explain concepts far better than the IMO dreadful Typesafe documentation. The twitter school, for instance, will at the very least give you names for features that, if you saw in code, you'd not be able to easily search for, due to their very generic syntax: For instance, context bounds. Another good set of blog posts comes from Bill Venners in the Artima website.
Functional Programming in Scala is amazing. Highly recommended even for non scala programmers.
Second, come check out the #scala channel on Freenode. It's fantastic, has a REPL bot so you can show everyone in your compiler issues and get realtime help, tons of people, always active, very beginner friendly. Give it a shot.
Unless somebody like Tony Morris needs to feel better about his day. The average IRCer is really nice but (at least when I was over there) there is an ugly and abusive side that almost burned me out on Scala.
Echoing any recommendations for 'Scala for the Impatient' - it is a fantastic beginner/intermediate book that gets you productive pretty quickly, so much so that I'm planning on having an intern who has no Scala experience go through it this summer.
Have you used any imperative, statically typed language that's compiled, such as C#, C++ or Swift? Previous knowledge of a purely functional language would be useful as well, but not required. Knowing Java helps with debugging and working with libraries built from Java, which depending on what one is doing (Android for example or using JSoup for scraping), is inescapable. You'll end up having to semi learn Java along the way, at least from what a friend told me (I already knew Java previously, so cannot comment on that). Scala, like C#, has extension methods to make dealing with Java libraries easier though, but it still doesn't solve things like JDK annoyances (type erasure).
If you're only familiar with scripting languages, it's going to be sort of a leap into learning Scala and could be done I think, though probably not the language I would recommend starting with since it's easy to abuse. The syntax is nowhere the same, but Scala sort of reminds me of the "Perl of statically compiled languages" in that you can write some really obtuse code without even trying if you're not careful. I don't think that's a bad thing necessarily, because it's a language that gives you a lot of flexibility (and more than enough rope to hang yourself). If you work with someone else, be sure to discuss some sort of agreed upon standard to using Scala, else you'll end up with some messy code.
Scala looks a bit like Python in parts as well as Swift, but I consider it more closer to a progressive version of C# with F# mixed into it.
Unfortunate given that my advice is sort of based on Java...
When I was learning Scala, I was intimidated by a lot of the syntactic sugar that it had. It's a calming effect to realize that all of that desugars into very simple, regular things. Java happens to be a very regular, unsurprising language.
So despite how surprising/special Scala may seem, under the hood it's just a bunch of methods.
There will be an acclimation period where you eschew the fancy stuff and stick with the Java style. But as you encounter the same structures and pain points, you will begin to see which Scala structures you like and will become comfortable with.
Find a style guide. Don't go crazy with point free. In general, it's a bad idea. (It's good if your DSL is super sexy/robust/easy to understand)
Do you prefer to jump in at the deep end or to ramp up gently? F# is a more elegant language that will force you to go straight into functional style; Scala is a bit of a hodgepodge but you'll be able to write code that's very similar to Python, at least to start with.
> it's exactly the same code that gets run on Scala-JVM
That can't be exactly true, since "Awaitable"  doesn't appear anywhere in the scala-js codebase. So I guess as long as you don't mention that trait by name, or attempt to block on a future, then your effectively duck-typed Scala-JVM code will be able to run unmodified on Scala-JS.