If something goes wrong by running the emulator, you may receive the message “not ready” for the device “forever”. Even if everything is going fine, it may take about five minutes or so to start sometimes, especially after you clear the user data. Kill the attempt to launch or debug (find the red square) and start the emulator from the AVD manager, and then wait for it to go to the main screen before trying to start or debug your application.
Usually I start my work day with Android by running the emulator from the AVD Manager (sometimes I run more than one if I test different devices / versions of Android, etc.), and then leave them all day. If your program does not do something really terrible, starting another debugging session will terminate the old copy and install and start a new one, so there is no reason to start and stop the emulator.
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