You ask if you could take it for a spin to try it out.
Tell them how cool their dragon is.
When the trainer isn't looking you steal it.
You gaze at it and think how much better it would be than your dragon.
You try to kidnap it and train it to become yours.
Go to Hiccup and tell him to put it in the Book of Dragons.
Write it down in the Book of Dragons
Take it for a spin.