How do you do a stoppie?

Answer 1

It is a difficult job. Make sure you are wearing all the protection gear for unfortunate accidents.
You need to practice for some time. Its about right braking of the front wheel and correct body weight transfers.
You should be holding the handle bar for bike straight for practices. Drive at some slow speed which seems controllable ( 20km/h) and then Press front lightly brake while slowly shifting your body weight to the front. Slowly and steadily you can start increasing your speed to 25-30km/h ( ideal speed to learn stopie) and start increasing the amount of break you apply. Make sure you don't press it too much.
I will though suggest you to ask some professional in real life. This will provide you correct guidance while you do it. You can also watch videos to know how to do it.

On the other hand :
In Gta Vice city you are required to press brake and lean forward button to do a stopie.