Use a tripod or lean against something
Getting yourself a steady hand is the first step in getting a quality photo. Lean against something stable, like a tree. If you have one use a Tripod, they are fairly cheap and worth the investment!
Turn off flash
Turn the flash off and use HDR mode. Flashes are only useful for to illuminate something a few feet in front of the camera. Fireworks are bright enough, flash is unnecessary. HDR is basically taking a series of photos with different levels of exposure and combines them all into one photo. If you want a more vivid picture, try it out!
Use landscape mode
Rotate your phone so that it is sideways and take a landscape oriented photo to capture the full sky.
Avoid using the digital zoom
Go back later and use the crop tool to rid the picture of objects you don’t want. Digital zoom can often make the image blurry.
Less exposure the better
Decrease the exposure or brightness. This will allow you to take a picture of a firework without overexposure.
Disable the ‘Review Pictures’ setting for Android users
Usually after you take a picture, your phone will automatically display the photo. Since fireworks are quick, turning this off will allow you to take more pictures.
Take the picture!
Experiment with live & burst
You could also experiment with live pictures and burst photos. To take a burst photo, hold down on your shutter. The burst will take many photos all at once, so you are bound to get a few great shots!
Try out the editing tools
After you have shot your photos use an editing tool to increase contrast, brilliance, shadows, and other effects. Don’t be afraid to play around with it, you never know how cool it could turn out!