First time I gave a presentation, an experienced speaker congratulated me afterwards. I said that I’d had to rehearse the talk 5 times before I gave it. He said he still rehearsed his 10 times.
I taught technical courses. A ground rule I had was 3 hours rehearsal for 1 hour of content. A 1 week class meant 3 weeks of practice. I still think this is what separates the bland teachers from the great ones.