It may surprise you that our face hides subtle but substantial tension tightening the larynx and preventing it to smoothly pull the vocal cords to pitch. One of the first step in effortless singing is to identify which might be holding you back. Executed under the pretext of soulful expression, we engage too many facial muscles unnecessarily.
1) Raising Eyebrows
It is fairly common for untrained singers to raise their eyebrows as they ascend in range. As if eyebrows could lift pitches up. This in fact raises the front of the larynx and makes it challenging to cross the vocal break. People who do manage to make it through head voice while raising eyebrows, often end up having to push a lot more in order to do so; a potential hazard for fragile vocal cords. A raised larynx also produces a thinner tone closing the door to full voice. Get rid of this habit by placing a hand on your eyebrows and feeling whether or not they are staying put when singing higher.
2) Frowning
Some singers tend to frown as they are concentrating really hard on their skills. Frowning squeezes the larynx in such a way that it can't adequately tilt to enter mix voice. Watch yourself in a mirror to keep your facial expression neutral before you can eventually show emotions that convey the meaning of the text.
3) Engaging Lip Corners
I call this one the "Jocker face". In an attempt to enunciate, many singers including pros excessively engage their lip corners on"Aw". "Eee", "Eh" and "Ae"sounds. As discussed earlier, the back and forth required tilting motion of the larynx is altered by putting stress on it. Always open your mouth vertically by dropping your jaw as opposed to horizontally. Relax your lips!
Still not convinced that these facial tensions affect your voice? See for yourself by holding a note on a comfortable pitch and alternatively raise and lower your eyebrows. Frown and relax. Engage your lip corners sideways then let go. Do you feel anything happening to your larynx? Told you so! It takes time to create new muscle memory. Be patient with yourself and you'll succeed!