Your phone is probably the easiest camera to whip out at a moment's notice. To shave precious seconds off the launch time of your camera, double-tap the power button on your device.
Most Android phones have some method of quickly launching your phone, like the Moto X's shake gesture or the shortcut on your lock screen. As of Android Marshmallow, however, all Android phones can launch the camera with a double-tap of the power button (unless a manufacturer removed the feature for some reason).
It's easily one of the quickest ways to launch the camera app, no matter what you're currently doing with your phone. You can check out the How-To Geek's post below for more Android shortcuts you might not be using.
The Best Android Shortcuts You're Probably Not Using [How-To Geek]