First read:
http://monroeworld.com/android/subsonic/
Never use port 80 - ISP's often use it or block it. 8080,8081, work fine.
In Subsonic Settings/Network - UNCHECK " Automatically configure your router to allow incoming connections to Subsonic (using UPnP or NAT-PMP port forwarding)." make sure to hit the SAVE button, you may have to scroll down to see it depending on your screen size. UPnP or Plug & Pray works sometimes, but not very often and you're better off learning what's going on anyway. You're dipping your toe into the network mgmt. thing anyway, might as well learn what's going on as home networks don't get simpler as time goes on. As your network gets more complex, you're going to have to learn this stuff! No time like the present.
Manually assign a fixed intenal IP and static route to your server at the upper end of the address range of the router, out of the way of DHCP, e.g. 192.168.1.254
Set up your router manually. uPNP might work, but most often it doesn't. Learing how to do it will be a skill you'll love having as your network grows.
Check the Subsonic Control Panel to make sure it's using the right port you're going to use. I typically use 8080, 8081, etc.
Set up port forwarding in your router to direct traffic on the selected port to your server.
Learn your external IP address assigned by your ISP.
Test your setup by entering your external IP:port# to see if it connects. e.g.
http://24.88.76.61:8080/ If it works, you're good to go.