Looking back at my own personal experience, I’m giving most of the credit to Clojure for busting my OO mindset. However knowing what I know now, I’d choose Racket instead (dealing with the JVM adds an unnecessary element of hassle - OK if you need it; otherwise avoid it). Some reasons for my opinion are detailed in these posts:
New to programming, how should I proceed in learning Elixir? - #18 by peerreynders
Will reading a Haskell book help adopt a functional programming mindset? - #9 by peerreynders
Opinions on Elixir vs. Clojure - #16 by peerreynders
One potential starting point is Realm of Racket as HtDP2e may feel a bit slow for an experienced programmer and SICP with DrRacket may be a bit academic (though Peter Norvig’s Amazon review is an entertaining read).
Then “practice” with something like exercism.io.
Once you feel that Racket has put a big enough dent in your OO mindset double back to Elixir with
Learn Functional Programming with Elixir (Pragprog)
at which point you should be much less tempted to approach Elixir in imperative/OO ways.
PS: Of course, you can try the pure Elixir path as already suggested - but I find that often a well established OO mindset needs to be approached with the equivalent of a baseball bat.
