One of the missions to reach level 34 in Alto’s Adventure is to “Land a proximity backflip.”
What is a proximity backflip? How do I land one?
A proximity backflip is a backflip performed while close to the ground.
The easiest way to quickly lengthen your scarf is to try for proximity backflips—these are backflips you do close to the ground.
The article suggests using Maya’s increased backflip speed to land proximity backflips early in the run.
There's a great place to do a proximity backflip right at the start of the game using Maya: After the very first hill, jump right at the flat before the second bend.