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A scale is a sequence of musical notes that either ascend or descend in pitch. Most scales are based around octaves, which are 8 notes that are each a half or whole step apart (do-re-mi-fa-sol-la-ti-do). Sing scales so that you can loosen up your tight, firm vocal chords. This will enable you to gain control and flexibility. An elevator slide is a warm up technique that allows you to travel from head voice to chest voice and back in a smoother way that prevents cracking. To do this, start singing the vowel "e" on a low note and then make a siren-like sound as you move to higher and higher notes. Then, go back down to the note you started on. After this, do the same exact thing, but with an "ah" sound instead. Make a list of four or five different songs you really enjoy singing. Then, rank them according to difficulty. Make a playlist that starts with the easier songs and ends with the harder ones. Warm up by singing each song on the playlist. By the time you get to the more challenging songs, your vocal chords should be more flexible and ready.
Start off by singing a few scales. Do elevator slides. Sing along to a playlist.