A few easily remembered suggestions are: 

1.  Rest the voice for an hour or two before speaking in public.

2.  Gargle the throat night and morning with salt and water.

3.  Never force the voice.

4.  Avoid all occasions that strain the voice, such as prolonged conversation, speaking against noise, or in cold and damp air.

5.  Practise deep breathing until it becomes an unconscious habit.

6.  Favor an outdoor life.

7.  Hum or sing a little every day.

8.  Discontinue public speaking when there is a severe cold or other affection of the throat.

9.  Rest the voice and body immediately after speaking in public.

DON’TS FOR PUBLIC SPEAKERS

     Don’t rant. 
     Don’t prate. 
     Don’t fidget. 
     Don’t flatter. 
     Don’t declaim. 
     Don’t be glib. 
     Don’t hesitate. 
     Don’t be nasal. 
     Don’t apologize. 
     Don’t dogmatize. 
     Don’t be slangy. 
     Don’t antagonize. 
     Don’t be awkward. 
     Don’t be violent. 
     Don’t be personal. 
     Don’t be “funny.” 
     Don’t attitudinize. 
     Don’t be monotonous. 
     Don’t speak rapidly. 
     Don’t sway your body. 
     Don’t be long-winded. 
     Don’t “hem” and “haw.” 
     Don’t praise yourself. 
     Don’t overgesticulate. 
     Don’t pace the platform. 
     Don’t clear your throat. 
     Don’t “point with pride.” 
     Don’t tell a long story. 
     Don’t rise on your toes. 
     Don’t distort your words. 
     Don’t stand like a statue. 
     Don’t address the ceiling. 
     Don’t speak in a high key. 
     Don’t emphasize everything. 
     Don’t drink while speaking. 
     Don’t fatigue your audience. 
     Don’t exceed your time limit. 
     Don’t talk for talking’s sake. 
     Don’t wander from your subject. 
     Don’t fumble with your clothes. 
     Don’t speak through closed teeth. 
     Don’t put your hands on your hips. 
     Don’t fail to stop when you have ended.

DO’S FOR PUBLIC SPEAKERS

     Be prepared. 
     Begin slowly. 
     Be modest. 
     Speak distinctly. 
     Address all your hearers. 
     Be uniformly courteous. 
     Prune your sentences. 
     Cultivate mental alertness. 
     Conceal your method. 
     Be scrupulously clear. 
     Feel sure of yourself. 
     Look your audience in the eyes. 
     Be direct. 
     Favor your deep tones. 
     Speak deliberately. 
     Get to your facts. 
     Be earnest. 
     Observe your pauses. 
     Suit the action to the word. 
     Be yourself at your best. 
     Speak fluently. 
     Use your abdominal muscles. 
     Make yourself interesting.