Common problems in vocal delivery during a presentation include the voice sounding;

aggressive
unconvincing
bored
emotional
monotonous
Here are some basic tips from a Professional Voice coach that may help you to improve your vocal delivery.

Before giving your presentation:

Be well prepared and rehearsed - write out your text in full, reduce to note format,
Rehearse your speech aloud making eye contact with your audience.

Look after vour voice! - Drink plenty of water the night before - avoid red wine cheese and anything with caffeine.

On the day:

Remember to breathe - in a pressured situation, the untrained voice can become constricted, and the breathing shallow.

Find your balance - knees unlocked, head up and shoulders released down.

TBS sequence - think, breathe, and speak!

New Thought, New Pitch - vary your pitch to convey a new point or message