Now use the iron. My technique is to use a fairly firm pressure, although others have gotten good results using very little pressure.

Make sure to spend time along the edges, as this is where most PNP failures occur.

It also helps to spend part of the time with the iron just sitting flat on the entire sheet.

I usually iron for 3 to 4 minutes, alternating 30 seconds of the iron sitting flat with 30 seconds of firm pressure while moving the iron.