At first, let's see if you're interested in the topic or not. To grasp a big picture about concurrency, best practice is to take a look at operating systems books, like Operating systems internal by Stalings or Modern operating systems by Tanenbaum. They can give you an intuition about what this is all about.
There's also an old book, named Concurrent programming by Ben-Ari. If you found it, it can be helpful.
Beside reading text books it's good get your hands dirty by writing some concurrent programs. Python is a very good choice if you want to start using threads. Every Python book has a part dedicated to this topic. Also a with a simple search on the web you can find a lot of resources about it, but I give these two higher preference:
Multithreaded Programming (POSIX pthreads Tutorial), A very comprehensive introduction to concurrency and multi-threading. It's mainly about C multi-threading.
The other one is Thread Synchronization Mechanisms in Python.
Now if you still find yourself interested about concurrent programming, it's time to go deeper. You almost have the basic knowledge of concurrency, now the best approach at this point is to start solving problem and become familiar with patterns. To achieve this goal, you can use The Little Book of Semaphores. It's one of best books in the field and it's also free. This is a book that can head you toward becoming proficient at concurrent programming.
These should be enough if you want to approach concurrent programming, but if you have enough time, and you're eager, it's good to take a look at some other paradigms of concurrent programming, like actors which are used in Erlang. I say it is worth to read some chapters of the book Seven Languages in Seven Weeks, especially chapter about Erlang and IO. At first glance, it might be hard and strange, but it's good to become familiar with other solutions to concurrency.
