The best onboarding videos demonstrate your product’s benefits and answer your users’ most pressing questions, so they can hit the ground running.
a super onboarding video :
- Whether it’s a genuine, warm welcome or a clear explanation of a solution to a user’s problem, something will spark a sudden realization that they’ve found the right fit.
- show the humans behind your product, better even if you show users
- demo the product
- learn about your audience

Remedies for nose engagement drop:
Abbreviate the introduction to the material. Get to the point, already!
Make sure your audio is audible and clear.
Experiment with removing intro graphics and logo sequences, especially if people are likely to watch a bunch of videos in succession.
Hook your audience by showing and proving your point, rather than just stating it.
Avoid talking about yourself too much. Instead, the page the video lives on can help set context for the video.

Remedies for body engagement drop:
Consider splitting the body into multiple videos.
If the concept allows for it, use different shooting locations to break up the monotony.
Think about adding comedic or human elements to longer sections.
Remove section title cards. This will force you to tighten your section transitions and will make the video feel shorter.
Try adding another person to the script. Sometimes the flow of a video is better with two people speaking lines back and forth.
The right music can help drive the video and move the video along, keeping it from feeling stale.

At the end
Remedies for tail engagement drop:
Don’t use phrases like “in summary,” “that’s about it,” or “to wrap things up.” This is an indicator that the good information is over.
Avoid recapping everything you just said. The viewer can re-watch the video if they want to hear any information again.
Watch out for how long your logo is on screen at the end of the video. Use a short logo at the end of the video, so that any calls to action or email collectors come up as soon as the video truly ends.
Watch out for music that clearly indicates the song is wrapping up and the video is about to end.

Source : https://wistia.com/learn/marketing/understanding-audience-retention#remedies-for-nose-engagement-drop