I got most of this information from this blog post and video:
First, you have to have the Windows Phone SDK downloaded on your computer. Next, you will need a Windows Phone Developer account (or be registered as a developer, which typically comes with a cost). You’ll also obviously need a Windows Phone 8, and a UBS cable.
You’ll then need to register your phone as a developer device. Search on your compute for “registration”:
That brings up this little app (and this assumes you have a Windows Phone connected to the computer via USB cable):
The video I mentioned above covers a few different scenarios. You might see a couple of different errors on this screen before you can go on. I didn’t have any, it just worked for me. Once those are resolved, you put in your Live credentials and the phone is unlocked.
Now, to deploy your app to your phone, search for deployment:
which brings up this app:
You simply browse to your .xap file (your compiled WP8 app) and click Deploy. That’s it!