When removing the sensor/front assembly, there will be a small, black, plastic spacer which you'll easily lose. When assembling, the spacer should be between the front facing camera and the 2 contacts. Make sure the flat side is on top (i.e. facing to the back of the phone when assembled), and the opening is towards the phone bottom and towards the opposite side of the volume buttons.

Furthermore, my replacement screen did not come with:

1. The translucent, circular protector for the front cam

2. The square metal bracket for the sensor

3. The small white plastic sheet in front of the other sensor.

I manually transferred those parts to my new display assembly using a hairdryer (to loosen up the glue), tweezers and some ordinary glue (the ones they have in kindergarten, not the permanent glue)

When reassembling, make sure to disconnect and reconnect the battery (i.e. power cycling the phone). Sometimes a new screen won't work before power cycling the phone.

Watch out while removing the home button cable. It breaks really easily! In my case I ended up with a fold in the home button cable, but luckily it still worked.

You really shouldn't complete this step without using a hairdryer or something else to heat up the glue!