There are two permission that usually give us problems:
<uses-feature android:name="android.hardware.camera.autofocus"/>
<uses-permission android:name="android.permission.CALL_PHONE" />
The first one uses a camera function that some tablets and smarthphones wont have.
The second uses the phone function, which non-phone devices (tablets) won't have.
To solve this you must add this to your manifest:
<uses-permission android:name="android.permission.CALL_PHONE" />
<uses-feature android:name="android.hardware.telephony" android:required="false" />
<uses-feature android:name="android.hardware.camera.autofocus" android:required="false" />
Uses-feature has a higher "permission level" them user-permission, so use use hardware.telephone but with required false, which means non-phone devices can install de app.
The same for camera.autofocus, its request, but it will not prevent the device from installing the app (required=false)
Just remember that if you start an call intent on a non-phone device it will crash, you must use a try catch for these functions.