Write the opening line last, and iterate on it hardest
A video has roughly the first couple of seconds to earn a viewer's continued attention, so the opening line deserves more revision than any other line in the script. Write the body first, then work backward to the strongest opening. That produces a better hook than trying to nail it before the rest exists.
Write for the ear, not the eye
A script that reads well on a page does not always sound natural spoken aloud. Read a draft out loud before filming. It catches stiff phrasing that looks fine written down and sounds wrong out of a mouth.
Plan for captions from the start
A large share of viewers watch with sound off, so a script should work when it is only read as on-screen captions. That affects sentence length and pacing: long, complex sentences are harder to follow as scrolling captions than as spoken audio with full attention.
End with a specific, singular next step
A script that closes with one clear call to action converts better than one that ends vaguely or asks for several different actions at once. Decide the single most important thing a viewer should do next before writing the ending.