Treat your talk like a piano concert, not a first reading
Schedule run-throughs, check yourself on video, and drill the start and finish until they hold.

Speaker coach Montana von Fliss has a blunt test for anyone with a talk coming up. Imagine you receive new piano music on Monday for a Friday recital. Would you only read it silently all week and then perform it cold?
She says speakers do that exact thing all the time, and practice fixes it.
Her method starts with practice with purpose. Put a rehearsal schedule in your calendar, give yourself a small treat for each run-through, and layer in one skill at a time. When the event is a week away, she advises a full spoken run-through every day.
By practice, she does not mean rereading notes at your desk. She means getting on your feet, speaking aloud, picturing your listeners and welcoming them in, and clicking through your slides much as you will on the day, whether virtual or in person.
If you are not sure you look confident, she says to film yourself and review the footage. She knows most people hate watching themselves, but she asks whether you would rather make that adjustment before you are in front of your audience, while keeping it your version of confident.
Short on time, just take the start and the finish and repeat them back to back three times, wherever you happen to be. She suggests fitting in the reps in the shower, while walking the dog, and while cooking dinner at home. She says her own kids are very used to hearing her walk around the house talking to herself. Do not worry about overpractice, she says, because you can drop a word for word script if it starts to sound robotic and use bullet point notes instead, which remind you what to say and let you vary the wording slightly on each pass so it stays lively.
Questions people ask
How much rehearsal is actually enough?
Von Fliss advises a full out-loud run each day during the week before an event, plus extra reps of the opening and closing. She recommends putting the sessions in your calendar and giving yourself a small treat for each run-through.
Why focus so much on the opening and closing?
She offers it as the short, repeatable fallback for when there is no time for a full run-through. You can run just the opening and closing three times in a row from anywhere, which keeps preparation going in spare moments.
Will practicing that much make me sound robotic?
Von Fliss says not to let fear of overpractice stop you. If a word for word script starts to sound robotic, let it go and work from bullet point notes. The notes remind you what you want to say and allow slight variation each time.