HPLIP doesn't support this printer (yet?) out of the box, so here the steps to get it running using foo2zjs. For more info please visit http://foo2zjs.rkkda.com/
-Pair the printer with your Network using the wps key
-The driver I used was foo2zjs, for that to work we need to install a few things.
-Open a terminal:
sudo eopkg it -c system.devel
-Download the driver(you might want to change to your downloads folder for that ):
wget -O foo2zjs.tar.gz http://foo2zjs.rkkda.com/foo2zjs.tar.gz
-Unpack the driver:
tar zxvf foo2zjs.tar.gz
sudo make install clean
After that just open http://localhost:631 in a browser, navigate to Administration -> Add Printer. The M12w should be there under Discovered Network Printers. Select it, continue and select "HP LaserJet Pro M12w Foomatic/foo2zjs-z2 (en)" from the list, it should be listed under manufacturer HP.
That's it. You should be able to print over network.
At first glance it looks like Cups is using a static IP for the printer, so it would propably be a good idea to give it a static IP in your router's configuration....
Edit: updated title to be more search engine friendly/fixed typo