Here are some tips for all cameras:
Clean the lens. Over time the camera lens can collect lint (and fingerprints) and create a blurred image. Just give it a good wipe with a clean cloth. And check for scratches while your at it. If you do have scratches scrap the idea of photos. You'll have to fit a replacement lens or get a new camera.
Avoid subjects in low light, at least if you want them to be consistently lit. The small sensors in camera phones cannot run at high ISO speeds (i.e. high sensitivity to light, permitting indoor photos without a flash) without introducing large amounts of noise. In most circumstances, this precludes indoor photos other than in the best-lit places.
Avoid bright reflections, and other "hot-spots". This will either force the camera to under-expose the rest of the shot, or cause the camera to blow out the highlights on the brightest parts of the shot. The latter is worse, since it is sometimes possible to extract details from parts of the image that are too dark, but impossible to recover blown highlights (since there is no detail therein to extract). On the other hand, this can be used to artistic ends, such as with bright light streaming through a window. People pictures will look best in diffuse lighting such as open shade, under a cloudy sky, or in bright artificial light. Try to include bright colors, which will show up well, rather than a range of light and dark areas (which will both lose detail).
Set your phone to its highest picture quality and resolution. You might end up taking a shot that someone may want to publish in a magazine or a blog; you won't be able to do this if you only have a low-resolution version of the photo.
Turn off picture frames. A normally great shot may be ruined by a cheesy frame or background. Halos are something that I particularly don't like. But to each their own.
Turn off any other effects. These include black-and-white, sepia tones, inverted colors, and so on. These aren't as necessarily as cheesy-looking as frames and have their place; nonetheless, these things are much better done in photo editing software later on than on board the phone. People on Etsy don't want to look at a vintage vase in sepia. how will they know what color it actually is?
Set the white balance, if your phone supports it. The human eye usually adjusts for lighting, and so white appears white in any kind of lighting. A camera, however, will see that a given subject is redder than normal under normal incandescent household lighting. Better camera phones will give you the option to adjust the camera for this. If you have such an option, use it. If you're not sure what setting to use, experiment.
Use your flash judiciously. If you find yourself using a flash because your whole scene is insufficiently lit, you're probably taking photographs indoors in poor light. Don't do this, and go back to the first step; a scene lit entirely by your flash will look un-natural, since on a camera phone it is not typically possible to aim the flash anything but directly ahead (i.e. you can't bounce it off ceilings or walls, as with dedicated flash guns for SLR cameras). On the other hand, a flash is a good option for filling in shadows in harsh sunlight. I've found that flash is never acceptable and you shouldn't need one in a light box
Frame your shot. Make sure that everything you want in the shot is in the picture, and ready to be captured. Some phones show the entire viewfinder, meaning that what is on the screen is exactly what will be captured in the image. Other phones, however, only show what is in the middle of the image, but will capture more than the viewfinder shows. Err on the side of putting too much empty space into your picture; you can always crop it later.
Take several pictures. You might only take one photo of each view to save time only to find that they're blurry. And putting everything back up takes more time than if you just took some extra shots.
Turn on macro if you have it. (The icon is a little flower.) Close up shots, esp. jewelry always look better in macro mode. Don't have this mode? Set your phone to auto and let it focus.
Zoom it in. If you're taking photos in a light box and lean in you're going to get an unsightly shadow that's impossible to get rid of. (This plagues me.)
Take the glass out of picture frames. It helps get rid of those glare spots.
That's all I can think of for now. I'll try to post more later.
Hope this helps -Michelle