I am hoping that you have already installed an app named 'MyPhoneExplorer'.
If you have, all you need do is start the desktop version and connect the USB cable.
MyPhoneExplorer bypasses the screen lock and allows access to the files directly on the device.
You will NOT be able to operate the phone, just retrieve data that you want to save.
I know from experience that if the screen is locked, you are out of luck.
Neither Kies or SideSync will work until after you unlock the screen on the phone.
Now, go find someone who can install a replacement or loaner screen, The link above shows how to make the phone work again.
A word of Warning to all reading this thread.... install 'MyPhoneExplorer' on your Android device now, not later after you wished you already had. Once the screen is broken, it is too late.
=>
* MyPhoneExplorer works even when locked and can't access screen