Fix 1: Tap the iPhone
Use the palm of your hand to tap the top of the iPhone (rear camera lens end). This method solved so many iPhone users issue.
Fix 2: Press and hold the iPhone camera button
Press and hold the iPhone camera button until the Camera is focused. Release the button when image becomes clear.
Fix 3: Remove the iPhone bumper/ case
Remove the iPhone bumper or metallic case when you using iPhone camera to take photos or videos. This might cause iPhone camera blurry or wobbly issue.
Also, make sure that the yellow box which your camera is focusing on, is the partof the picture you want in focus. When the yellow box appears, you can tap a different part of the image to be the point that the camera is focussed on.