1. Protect your lens!!! I know this device is so easy to "throw" in a handbag with car keys and wallets, or for the men in pockets with change and keys, but I often say..."would you treat a $1500.00 DSLR lens that way? Of course not, it gets a lens cap then into a camera bag....so even though the mobile device is not a $1500.00 DSLR lens, if you want "sharp" images you must treat it so!
a. Use a Mophie Battery pack! It keeps the lens recessed due to the packs design, so if you lay it on a table the lens will not be vulnerable to scratches.
b. Put it into a protective cloth (I love my Vera Bradley Cross Body Pouch) or neoprene pouch before putting it in your pocket or handbag!
2. Clean your lens: I always use a micro fiber lens cloth to wipe the lens off each day I use it to capture images. I keep it in the pouch where I keep my phone stored.
3. Capture technique matters:
a. Don't use the volume button to trigger the shutter, when you push on the button you inherently shake the camera (or phone).
b. Shoot with an app that allows you to use a focus point on screen like Camera+ for maximum sharpness, and remember to use it.
c. Tap gently on the shutter button in the shooting app. There is no need to push hard on the screen on any shutter button: just a real soft gentle touch and release and it will fire.
d. Camera holding technique, I use a rock steady grip on my iPhone cradling it in both hands for maximum stability when I shoot, as if I was hand holding and shooting with my big camera, I also stabilize my body.
4. Processing technique:
a. I use Snapseed on every image I create on my iPhone sharpening them up to about 25% (no more). The sharpening feature can be found under the details filter menu in Snapseed. In addition every image gets a little bit of Structure, anywhere from 10-20%, also under the details menu in Snapseed.
I hope these few tips, help you improve the sharpness of your mobile phone images.