Sorry this is a bit late in answering.
But if you see 0.0 as the output, that means that the joystick inputs are being read, and they're showing 0.0. Check your driver station setup interface to see if the Joysticks are plugged into the right usb locations.
Also, keep in mind that you should keep outputting values instead of doing it only once.
If you only println it once, this is what happens:
Robot starts -> get joystick value -> print value -> you move joystick.
When you move the joystick, the robot has already printed the joystick value. It won't update by itself, so you'll get the default 0.0
You should println it continuously. You could put it into the teleopPeriodic or teleopContinuous loops. If you just want to test it, you could run an infinite loop as such:
Code:
while(true){
System.out.println(leftStick.getX());
}