✅✅✅ On the left: standing upright with a small inclination forward of the torso.

The upper half of the arms stay attached to the torso angled to the ground, at this point only the lower half of the arms move.
Elbows might come a little forward, but as long as it’s not too much, that’s fine aswell.

❌❌❌On the right the classic gym bro who goes for the whole stack without even knowing how to properly perform the exercise.
Because the load is too heavy, his shoulders spike up and internally rotate during each rep because the scapulas cannot be locked down & back as they should.
Besides close to zero tricep gains, this can definitely cause troubles like shoulder impingement in the long run, so make sure not to do that.