This is probably a good book buy order (buy as many as you like, or 1, or 2, whatever)
- https://www.amazon.com/Well-Grounded-Rubyist-David-Black/dp/1617291692
- https://www.amazon.com/Practical-Object-Oriented-Design-Ruby-Addison-Wesley-ebook/dp/B00BXU85JO
- https://www.amazon.com/Eloquent-Ruby-Addison-Wesley-Professional/dp/0321584104 (a little old but probably still good)
- https://www.amazon.com/Design-Patterns-Ruby-Russ-Olsen/dp/0321490452
running a risk because I put a book at the top slot I haven't read ;)