Lift your voice
Raise your voice. Most people usually speak below their normal speaking voice. This does not work well for your communication skills. Gradually try lifting your voice to ensure you do not shout as you speak. If you voice is strained, you could cause major damage to your vocal chords.
Slow down your voice to create a rhythm
If you are in the habit of speaking fast, slow down your talking pace. Talking fast might not allow the other person to absorb what you are trying to say and that defeats the purpose of communication. Speaking slow also allows you, the speaker, to create a rhythm. This rhythm will help you coordinate your voice to speak better. All great orators have speech pattern so you would do well to find your own.
This requires an understanding of your language of choice. Both grammar and lexicon should be on point to enable you enunciate properly. Speak with grammatical errors and wrong use of words and you will find yourself losing your audience.
Change your speech patterns
Do not maintain a single monotonous pitch when you talk. Vary your speech to make emphasis at various key points, add inflections to indicate a question or otherwise. Using a single pitch will quickly bore your audience. There is a reason why we read to children and change your voice for every character in the novel; it keeps the child interested and invested in the story.
You will need to practice your speaking voice to get comfortable and find that right speaking voice for you. Try recording your voice as you read books of various levels of complexity so you get an idea of your progress. You can watch video clips of various good orators to help you find you own pace. Some experts even recommend singing to get you comfortable with your own voice. You can also try vocal exercises; a good voice coach can also help you practice.
Maintain good posture
Ensure your body is positioned in a way that will ensure you lungs have proper air to push your words out. A good body posture keeps your body relaxed and relieves your body off undue strain as you talk.
Match you facial expression to your voice
Learn to convey your emotions through your speech. Your facial expression will help to convey this. If you smile, your voice will carry the emotion likewise if you express any other emotion.