For ironing you should use a hard underlay, otherwise the result will be ugly.
I used a sheet metal.
Before ironing you should test the position of the complete motive on the cloth - still handle wiht care.
Turn off the steam. Iron as hot as your t-shirt supports ;)
Iron the parts seperately.
Be sure to have everytime a baking paper between iron and toner.
At the beginning heat the complete part with the iron evenly.
Then go on from the border with some pressure, maybe use the edge of the iron.
While doing this, strip off the baking paper slowly - you will see wether the toner is on the cloth or on the paper -> should be all on the cloth.
Do not iron directly on the toner - the toner loves your iron much more than your t-shirt.
At the end all the toner should be on the cloth - nothing on the baking paper.
(the toner is black plasitc powder which melts on heat)