Stand with your feet shoulder-width apart. Shake your legs out a few times. Roll your shoulders a few times to loosen up. Bend forward and touch your toes, if you can, to flex your spine. Then rise slowly back to standing position. Stand on tiptoes. Imagine your head on a string tied to the ceiling. Come down off your tiptoes and try to leave your head where it was, so you are standing nice and tall.
According to the vocalist.org website, you can explore different mouth shapes and sounds to get different vocal feels. One technique you can try is to soften your voice, reducing volume and intensity of attack. Bring your voice almost to a whisper-softness. This way, you will achieve a "breathy" feel. This can be a great way of expressing milder emotions while singing. Alternatively, you can use the breathy voice to expand the dynamic range of a song.
Many singers practice the fire siren technique to improve the fluidity and range of their voices. Start by singing the lowest note you can hit. Then rise through your vocal range as smoothly as you can, making one long sliding note rather than a number of individual notes. When you hit your highest comfortable note, slide all the way down to your bottom note again.
Even professional singers fear being unable to hit very high or very low notes, especially when the notes are at the ends of their vocal ranges. A couple visualization techniques can help. As you sing toward those dreaded high notes, visualize them hitting the ceiling. Similarly, when attempting to hit low notes, imagine the notes striking the floor. Project your voice by visualizing every note striking the back wall of the room.