"A speaker needs three qualities...
- good sense
- good character
- and goodwill toward his hearers"
I can't help you much with character but here are some thoughts on the other two.
Have the good sense to:
- not read your PowerPoint slides
- cover only the material that your audience can absorb
- banish 'um' and 'you know' from your delivery
- know what your audience already knows
And have the goodwill to:
- respect your audience enough to rehearse your presentation before delivering it
- not argue with someone who asks a question or challenges your position
- make eye contact to relate on a human level
- smile to let the audience know you're glad to be there