What are good resources for learning more about communications?
Phraseology is standardized by the ICAO (but countries can notify differences to the standard) in Annex 10 and other documents. The ICAO quick reference guide presents phraseology examples for various situations (taxi, approach, emergency,...). If you are interested in recommendations concerning radio communications in general (not just what directly concerns the pilot), Eurocontrol released a European Action Plan for Air Ground Communications Safety.

Many CAAs also have some form of phraseology reference manual available for free. The general procedures and the phraseology will be almost the same from one country to the next, but variations do occur. 


US: 


The AIM has a section dedicated to radio communications which details procedures, phraseology and provides general recommendations. Communication examples illustrate the general principles. 
The FAA also published an order prescribing ATC procedures and phraseology (but this is a very dry read. Not where I would start)
The Instrument Procedures Handbook contains information regarding radio communication procedures specific to instrument flying (e.g. how to receive a clearance at a non-towered airport)

EU:


Eurocontrol released a guide to phraseology for GA pilots describing good communication practices, phraseology for different flight phases and aviation acronyms. It also has pictures (picture books are always better ;-) ).

UK:


The CAA release a radiotelephony manual describing the phraseology for different flight phases with examples at the end of the manual. It also describes the differences between ICAO and UK radiocommunications procedures (eg FL ONE HUNDRED instead of FL ONE ZERO ZERO). 

France:


The SIA has a phraseology training manual with phraseology examples for each flight phase and for using different flight services (ATC, AFIS,...)
The official text for radiotelephony with phraseology in French and English

And many more...




Knowing the phraseology is one thing, but understanding what is being said on the radio can be quite difficult. If you want to practice listening to and understanding radio exchanges, you can find ATC recordings on YouTube or go to LiveATC for ATC communications from all over the world.