Sometimes I have to be brutal, so here it is: if you are not practicing before a big presentation and don't want to start, there is no help for you. Period.
You may resist practice because in your experience it doesn't work anyway, and it's such a colossal pain.
That's because you're probably not practicing the right things in the right way.
The Dos and Don'ts of Practicing:
Do over-rehearse the introduction and close of your talk. People remember the first and last things you say, so say them with power.
Don't practice the whole talk over and over. It's usually unnecessary and frustrating.
Do practice delivering your greeting and your name with confidence. Really. It helps.
Don't thank them for coming, unless culturally you have to. It can sound self-deprecating.
Do practice out loud, on your feet.
Don't practice in the car, or at your desk. It is a waste of time.
Do practice eye contact; use more than you think is appropriate, and more than is comfortable.
Don't practice in the mirror.
Do practice using visual aids so you don't read from slides and lose all eye contact.
Don't hold pointers or clickers or pens or notes, or anything else in your hands. It prevents you from using gestures.
Do breathe and be kind to yourself!
Don't skip practicing!