Stand or sit up straight. If you are sitting, sit near the edge of the chair with your back straight. Ensure that your neck stays free and loose to reduce any tension in the neck area. Your shoulders should be relaxed and slightly back.
Practice using your stomach to push out air. While the diaphragm is normally an involuntary muscle, it is possible to control the diaphragm to help regulate your airflow and push air through. Practice breathing in and out using your diaphragm. Expand your diaphragm to breathe in and contract to breathe out.
Say the sound "tu" with your mouth. Practice saying "tu" several times until it feels comfortable. Once you get the movement down, practice mimicking the motion of the word "tu" without actually saying it. This is the proper way to tongue.
Breathe from your diaphragm and expel the air using the muscles in your diaphragm to push the air out. Mimic the sound "tu" while playing the flute. Practice slowly until it becomes comfortable for you.