From the Nokia Conversations article:
Keep very still
It’s fairly obvious that if you want to effectively take photos of fireworks you’ll need to do it in the nighttime, when it’s dark. This has some drawbacks when taking a photo, with one being that you’ll need to keep the shutter open for longer which will mean blurry photos if you’re wobbling about.
Depending on which camera phone you’re using, you might want to take a tripod. For example, you can buy the Nokia Camera Grip for the Nokia Lumia 1020 that has a standard tripod mount socket for an occasion such as this.
Or, if you’ve not got a tripod, position yourself so that you can stay as still as possible.
It may be possible to rest your camera on a table while you take the shot, or you could use the side of a tree or a fence post. Hold your phone against something solid to anchor it and stop from the gentle camera shake that you’ll inevitably have when holding it free hand.
The Lumia 1020 (etc.) all have OIS, but that's for making sure that 1/3rd sec exposures come out crisp, OIS can't help once you start experimenting with two second shots - so, yes, grab a tripod and a convenient mount. Yes, a table or wall might do, but in my experience the very fact that you're holding the phone at all introduces enough movement to ruin the shot.
The article continues:
Turn down the ISO
The higher the ISO number on your camera, the brighter the scene will be.
By default, the camera may try to compensate and turn up the ISO because you’re in a dark environment. However, a high ISO could introduce lots of ‘visual noise’ into your final shot, so make sure you manually turn it down.
ISO 100 is probably a good place to start. Experiment from there and turn it up depending on your scene.
A great tip this. What you want is low ISO - maybe even as low as 50, and then a long shutter time (this is set automatically on the Nokia 808 but is adjustable on the Lumia 1020), of a second or so.
Finally, and very important though usually forgotten by 'normobs':
Turn the flash off
There’s absolutely no point having the flash turned on when taking photographs of fireworks.
For starters, they’re way up in the sky and too far for the light to reach and the fireworks will probably be brighter than your flash, anyway.
Moreover, you’ll also increase your chance of taking a photo of clouds of smoke resulting in a less-than-impressive whiteout shot.
Absolutely. In fact, in some dusty climes, the Xenon flash is bright enough to reflect back off even particles of dust in the air, never mind smoke.
So if you're going for atmosphere at a fireworks display, think about how long the explosion or trail will be visible for, set the ISO as low as possible (the 808 includes an ND filter as well, so experiment with this too) and TTFFO. (Turn The Flippin' Flash Off!)
You can read the full article here.