I get asked this question frequently. I would like to share a few tips with you to help you get the most out of your cell phone camera.
Question one: Should I use the flash on my phone?
My general rule for camera flash is: Use it as little as possible. The flash is so close to the lens, light tends to shine straight onto the eye and illuminate the red retina in the back of your subject's eyes, for that demonic look. You know that look.
Nevertheless, if it's really dark, you simply have to use flash.
In low light, the flash mixes light from LEDs of two different colors, allowing it to better match the "warm" ambient light — especially indoors — and produces better-looking skin tones. It doesn't necessarily help with redeye, though. So experiment by taking photos slightly off-angle to your subjects.
Question two: How do I improve exposure?
Exposure is what it sounds like: The intensity of light the image sensor is exposed to.
The cellphone camera lets you specify where to optimize your exposure by tapping on that part of the screen when previewing your shot. (This will also set the focal point.) In a photo of a building against the sky for example, you can tap on the building to lighten up that portion, which may leave the sky too light. Or you can tap on the sky, which may leave the building dark. Use pattern (aka matrix or evaluative) metering, which sets the best exposure for the image as a whole.