I had the same problem, I had ordered a display plus adhesive here at iFixit shop, but there were no instruction how to attach it. I looked at manuals of other adhesives and found a proper way, that worked for me: Before reattaching the display cables I attached the adhesive on the phone, not on the display. At first you have to remove all old adhesive properly, if you have isopropanol you can use it to clean the frame. Then you remove the protective sheet (the side with the tab) from the new adhersive, place it carefully on the phone and press it with a spudger all around the frame. The protective sheet on this side is made of different parts so you can remove them on parts where you have to work on. Then you can attach the display cables and the battery cable and test if it works. If all works fine you can remove the last protective sheets and go on to attach the whole display unit.
