When you reassemble, make sure that you have the volume and power buttons in place, and make sure they are in the right position to line up with the switches on the motherboard. If they are not aligned, you risk snapping off the tiny switches on the motherboard (in which case, you are in for some soldering work).
There is also a piece of copper tape soldered onto the ribbon cable. Not sure if that's for grounding or heat dissipation, but I transferred it to the new screen also.
On my phone you have to flip up the black part of that connector (not the white part).