Clean the camera lens
Tap the subject to set focus
Hold the camera steady
Use a faster shutter speed
Increase lighting
Disable macro mode if not needed
Switch to autofocus
Recompose and refocus
Use burst mode
Check for motion blur
Stabilize with a tripod
Enable image stabilization
Avoid digital zoom
Update camera firmware
Reset camera settings
Test focus in a different app
Inspect the lens for damage
Get closer to the subject
Use manual focus if available
Replace a faulty lens or camera