I have difficulties with with debugging at Android Studio. After trying to launch application in debug mode device show alert with "Waiting For Debugger" title that never disappear. Also I have
android:debuggable="true", because when you run/debug an application in Android Studio is signed with a debug certificate so that setting is not mandatory.
Then check from console if the device is correctly attached with an
adb devices. You should see it listed.
Then try in this way:
1 - close Android Studio and any other IDE you have opened (maybe you have Eclipse also running?) and emulator instances;
2 - remove USB cable from PC;
3 - run
adb kill-server from console;
4 - open Android Studio;
5 - click on run/debug;
6 - when the window to select the device appears, attach your device to USB and USB to your computer;