Connect the new display and seat it in the phone, without removing the plastic for the adhesive.
Turn the phone on to make sure the display and home buttons work. If you glue the display without testing it first, it's a pain to take it off again once it has been glued and runs the risk of the display breaking.
If the display works, remove the plastic covering the adhesive and seat the display in the phone. Push gently around the edges to ensure a good seal