Write the promise first
Before any script, write one sentence that says what the viewer will have by the end. The title and thumbnail sell that promise, and the video has to keep it. Most drop-off in the first minute comes from a gap between what the title said and what the opening delivers.
Open inside the story
Skip the greeting and the channel introduction. Start at the most interesting true moment, restate the promise in plain words, and show that you will deliver it. The opening thirty seconds decide whether anyone sees the rest.
Re-hook on purpose
Every few minutes, give the viewer a new reason to stay: an open question, a result you have not revealed yet, a mistake you are about to show. Mark these in the script so they are planned rather than hoped for.
End when the promise is kept. A long outro after the payoff teaches viewers that the last minutes of your videos are safe to skip.