A very underrated exercise for effectively targeting the biceps!
The supinated variation in this demonstration does a great job at targeting both heads of your bicep for developing bigger peaks.
From the ground up, lean slightly forward in a semi tandem stance to help with balance.
Core tight, chest out.
The goal is to curl behind your ears. Slightly leading with your pinky's. This will incorporate the short head of the bicep.
Let your arms be completely extended before firing into flexion.
Repeat until failure of form or strength.
Make sure to start light and really feel out the exercise. Stay strict on your form and slowly work up just like any exercise, there's a great deal of stability required to properly perform this exercise.