I originally tried using an iOpener to heat the glass and melt the adhesive underneath, but finally had much better luck using a hair dryer about half an inch from the surface for 30 seconds at a time. If you expect significant screen cracking, you might consider covering the entire front with packing tape, as small slivers can fly upward.

As you may see in later pictures, it is probably best to start at a weak spot in the lower right corner of the screen, diagonal from the on/off button. Proceed around the screen, inserting and slowly moving picks or cards, but be careful along the top edge not to go too far to the left of the front camera, as I did.

In the third photo, you see the obstacles for breaking the adhesive along the top edge. From the rear-facing camera (square) to the front-facing camera (circle) there are three cables connected to the front assembly. You can also see where I dinged the LCD cable. The connector eventually just broke off from the trauma.