[parpfish]

if i'm giving a presentation, i always practice it several times and i always find flaws to fix up(there's no segue from this slide to this one, i need to reorder these so i can introduce X before talking about Y, etc).

but you have to practice the right way.

the terrible, long-winded, confusing presentations you've seen were most likely done by somebody that sees a presentations as merely "talking in front of a group" so their practice would be focused on memorizing lines/facts that want to say. they may sound polished, but it's not necessarily going to be good.

in order for your practice to actually help, you need to go through your presentation while maintaining a strong sense of empathy for the audience. you need to fight a constant battle against the 'curse of knowledge' and force yourself to honestly evaluate what you're doing from the perspective as a first-time listener.