I love using High Dynamic Range (HDR) to take pictures, particularly where there is a combination of bright and low lights, for example, a sunset. But every time I launched my Camera app I had to select HDR, which is annoying. Then I ran across the "Save custom camera" option. Just set all your camera settings the way you want it, then tap that option and give it a name (I called mine "HDR"). Since the Camera app launches to the last setting used, this effectively keeps HDR turned on for me.
This link has setup instructions for my HTC One M8, but is probably very similar to most Android phones.