1. Visual changeMotion, a cut, a transition, a sticker or a graphic on the very first frame.
2. Text on screenA caption or overlay that says what this is, readable with the sound off.
3. TensionA question, suspense or a surprise the viewer wants resolved.
4. Payoff promiseWhat the video delivers, matching what the title or thumbnail promised.

These are not steps in order: one opening can use several at once.