So you're doing a mockup in Photoshop, and you want to see it on your device. You've got to save it, email it to yourself, and open it on your phone, right? Not Anymore. Today, Google - well, Roman Nurik, a guy who works at Google - released "Android Design Preview," a little utility that will mirror your screen over ADB.
The app has a box that matches the resolution of your device, just start it up, stick it the alignment box over your Photoshop mockup, and you have a live preview of your work. Pretty cool.
It's a jar file, so it should work on PC, Mac, and Linux. You don't even need to push an apk to your phone, the program will take care of that.