During last night's storm emergency, I monitored the FDNY scanners to try and follow fast-moving and difficult-to-obtain details about what was happening where in NYC. For future reference, radioreference.com is an excellent way to do that (provided you have power and internet access). Along with that, you'll want to have two browser tabs open, for a cheat sheet on the codes the first responders use: Box Codes (find the location of the fire alarm boxes people use to get an FDNY response in an emergency), and FDNY 10 codes (shorthand developed in 1937 for common communication among first responders).
One good thing to keep in mind: not everything you hear on the scanner is confirmed fact. By definition, the first responders are often working with incomplete and unconfirmed calls for help, and chaotic situations. That, combined with the fact that it can be hard to understand what they're saying, make careful listening and sharing essential.