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Get all of your stretching done first before you start singing. Move your neck in slow circles to stretch those muscles, or switch between a big smile and an open mouth in the shape of an ‘O’ to stretch your face. Do each exercise 5-10 times to stretch your muscles well.  Bend your head back and flex your tongue outwards to stretch your throat. Do 5 big yawns to stretch the muscles around your mouth. Focus on one stretch if you don't have much time, or do 5 of each exercise to practice multiple stretches in one sitting. This is when you make your voice imitate the sound of an ambulance’s siren, moving up to the higher notes, back down to lower notes, and then back up again in one continuous sound. This will help you find out what your full range is while stretching your vocal cords. These help you reach your maximum high note by trying to imitate the high pitched noise of a siren. Arpeggios are useful exercises that help you transition from the different major and minor scales. Singing arpeggios to different vowels or other sounds is a great way to extend your vocal range.  Go online to find videos of arpeggio scales for you to sing along with, helping you practice. You might sing "ee-ee-ee-ee-ee," with the first and last "ee" being the lowest and the middle one being the highest note. Instead of being a continuous sound, arpeggios have very small pauses between each note. Vocal slides are a great way for you to gently reach high notes before coming back down. Use your voice to slide from a low note to a high note, and then back down as if your voice was on a swing.  Vocal slides are more controlled than vocal sirens, though they sometimes sound similar. Try humming your vocal slides or choosing a sound like “wooo” or “ahhh.” Vocal slides help relax your throat, making it easier for you to reach higher notes. While most of your early practicing should be focused on reaching the high notes briefly and then going back down, after you’ve mastered this skill, you can go even further. Once you reach your highest note, try to hold it for several seconds before going back down the scale.

Summary:
Stretch your facial and neck muscles to help your vocal cords. Practice vocal sirens to strengthen your high notes. Try arpeggios to practice your different pitches. Use vocal slides to slowly move up to higher notes. Draw out the high note once you reach it to practice holding it.