Relax your facial muscles by shaking your head back and forth, opening your mouth and allowing your lips to move freely, jostling as your head moves.
Warm up your facial muscles by humming and tapping your forehead and cheeks with the tips of your fingers vigorously, so that you feel the vibration of your sound in your face. Change to a "v-v-v" sound and tap around your lips. Repeat each massage about 10 times, lasting for about 30 seconds each.
Build your diaphragm and learn to project notes better by doing an exhaling exercise. Take a deep breath and exhale slowly, making an "s-s-s" sound (like mocking a snake), until your lungs are empty. Extend the exhale as long possible and tighten your stomach muscles as you release the air.
Use your diaphragm to push out the sound, rather than relying solely on your voice box (which you should relax), by squeezing the air from your lungs with muscle contractions. Practice singing notes up and down the scale.
Smile when you sing high notes to gain better control over voice projection. The higher the note you sing, the bigger your smile should be.