1. Anxiety is the enemy of pirouette!
A calm, relaxed state of mind will result in successful turns. Exhale as you press up into a releve. Gently but firmly push the back foot off the floor to start your momentum. Feel the opposition of the rise into releve and the pressing down of the shoulders. Keep your neck muscles relaxed so you can spot sharply.
2. Gripping is the enemy of extension!
Muscles that tighten the tendons surrounding your hip joints prevent the legs from fully extending. Drop the leg in the hip socket and find your full rotation, then extend the knee from there without sinking your weight into the standing leg or the knees/heels. And always exhale on the developpe.