It's grainy. That ruins a lot of my pictures
Take your picture settings off of auto during day shots;
Set ISO = 200 or 400
If looking TOWARD a source of light (i.e. the sun)
Set Exposure (EV or EB) = -0.5 or 1.0
If the source of light is BEHIND you, pointing onto your subject
Do not change the exposure
If you are not looking toward a source of light, and there is no direct light on the subject
Set Exposure (EV or EB) = +0.5 or 1.0
ISO is something you should always manually control - the more ISO, the more grainy the picture becomes. ISO is how the camera digitally increase the available light in a photo. With a DSLR you can combat this with Shutter Speed; the slower the shutter, the more the lens is able to capture available light, thus increasing the quality of photos (less grain). Higher end cameras can go to higher ISOs with lower amounts of grain (ISO is not created equally). However, slow shutter speed increase potential blur; moving objects or shaky hands, and slow shutter speed, do not mix.
This is just a straight forward response - I understand, and purposely left out, a lot more details and technicalities about what the different settings do, and how the effect the end image. This should be basic enough to improve cell phone pictures though.