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Drink warm water or tea with a slice of lemon when you get up in the morning and throughout the day. Don't drink a lot of sugar or caffeine, which can have a drying effect on your voice. Avoid milk and dairy products, which encourage mucus production. Warm drinks are best, rather than very hot or cold drinks. Green apples contain pectin, which can combat phlegm. Try drinking green apple juice or eating a green apple. Relax your shoulders, but don't stoop them or slouch. Keep your body erect but relaxed. Do posture exercises if it's hard for you not to slouch. Good posture gives you the best use of your abdominal-diaphragmatic breathing. Slouching pressures the rib cage which makes it harder for you to inhale. Open a window, if possible, to make the air you're breathing fresher. Breathe deeply into your lungs without raising your shoulders. Take breath into your nose for the count of three, pause, and then exhale in one big breath for a count of eight. Maintain a humidity level of at least 30% in your work environment. Run a humidifier, if needed. Breathe in steam from a personal steamer (available at drugstores) or a hot shower. Alternately, pour boiling water into a sink basin and inhale the steam. Inhaling steam moistens your voice box and can relieve irritation of the vocal folds. Don't inhale steam from directly over a pot of boiling water or a stove. Try wetting a washcloth in hot water, wringing it out, and breathing through it with your mouth and/or nose. Put the heels of your hands under your cheek bones. Rub the muscles of your face by pressing inwards and down. Let your jaw open itself as you massage your face. Do this a few times to warm up your mouth and lessen tension in your jaw. You can also use circular motions to massage your facial muscles. To hum, exhale with a light "hmmmm" sound at a low octave that's comfortable for you. Do this again, adding an "ahhh" sound for the second half of the exhale. To buzz your lips, purse them somewhat and vibrate your lips as you breathe out, with your tongue relaxed. Inhale, then trill with your lips again on the exhale. You can try these exercises at escalating and deescalating pitches. Hold your tongue behind your top teeth. Breath out, vibrating your tongue in the sound of an "r." Maintain the sound. Do this at various pitches, without going past your comfort level. This exercise helps your tongue to relax, while stimulating your voice and breath. Stretch your voice by starting in a low octave and moving upwards using the sound of "me." Don't force your range. Instead, use gentleness to broaden your range with each repetition. Also try this exercise with the sounds "e" and "oo."
Hydrate. Relax your posture. Control your breathing. Lubricate your voice with steam. Relax your jaws. Hum and buzz your lips. Trill your tongue. Go up and down octaves.