Here are the tips to improve your voice and speak fast and fluent
Breathe:
If you breathe in chest and abdomen your voice will sound very lower and week. But if you breathe from deeply from your nervous tackle a full-relaxed breaths will improve the depth of your voice and can help you sound more confident.
Take a singing or acting class.
Many your vocal warm take a singing class which helps you to improve your vocabulary and it brings the emotion in your words.
Watch your posture
Postures is the most important thing in your language. The way you stand and the way you sit reflects in your speech. So sitting and standing straight allows you to breathe properly ands it gives you a voice strengthen and clear (clarity)
Practice the tongue twister
Practicing tongue also improves your ability to speak clearly and it is also a exercise to your lips, tongue and face which gives a benefits to voice.
Example :
Nood likes nuts like a naughty noob
Six sticky skeletons
Excited executioner exercising his exercising powers excessively
Exercise your voice twice per day.
To improve your voice for speaking on a stage and for singing, you will need to exercise it on a regular schedule. Warm your voice before using it extensively, but also practice vocal exercises twice per day for best results.
Try setting aside 15 minutes to do vocal exercises when you wake up, or do them while you are getting ready for work or school. Then do them again before you go to bed, such as while you are making dinner or taking a bath.
Analyze your voice
Record yourself speaking or ask a friend to listen and analysis your voice. Check your volume, pitch, articulation, vocal quality and rate to where you need improvement. Is your volume is low or high. Whether your speech is clear to hear and understandable.
Show your emotions
This is an effective technique, if you notice some english speakers their speech reflects their emotions. The emotions quality of your voice express your strong feelings.
Drink plenty of water.
Be hydrate when your speaking for long stretch a time in high volume. It important to keep your vocal and throat lubricated.