If you're lucky, your screen will have some die cut adhesive on the back of it. If so, just peel off the protective backing on the adhesive, carefully fish the display connector through to the back of the phone, and carefully stick the screen in place. Emphasis on carefully, the adhesive they use is very sticky and you may only get one try.

My screen did not have adhesive on it, so I attached it using a combination of 3M 9474LE double-sided tape, and some "M-3035" liquid rubber adhesive that was left over from refoaming a pair of speakers. The exact liquid adhesive isn't critical but you want something flexible and fast curing.

To start, I cut a few strips of the double sided tape to fit in roughly the places where the original adhesive would have been, using the back of the old OLED as a guide. Peel away the paper from one side of the tape and attach it to the phone

Only apply tape to the metal frame of the phone, not on ribbon cables, the silver grounding contacts, etc.

Before applying liquid adhesive, peel the backing of the other side of the tape so it will be ready when you go to install the screen.

Since I couldn't cut pieces of tape small enough to get into some areas I also used a small amount of liquid adhesive around the edges. The key word here is "small amount", you don't want to get glue into the selfie cam, the speaker, etc.

Once the liquid adhesive has been applied, carefully fish the display connector through to the back of the phone and stick the screen in place. If any excess liquid adhesive seeps out between the edge of the screen and phone, you can quickly wipe this away with rubbing alcohol.