Hook them in the first 5 seconds: people click off very quickly. Make sure you do everything you can to grab them early. Also, if you are thinking of turning your video into an ad, products like YouTube TrueView are designed to let the user skip after 5 seconds.
Tell a compelling story: Video lets you evoke emotion in a user and when they come to purchase a product, they will rely on those emotions to determine which brand they go with. Brands often emotionally connect using awe, humour, shock, tears.
Video content: be regular, consistent, useful. So if you are creating video for content marketing, you need to make sure you pump out regular content. Check out FAQs in your area and design your content so that it will really speak to your niche and is the best answer to a question. Create a set up that you can replicate easily. A lot of YouTube stars record themselves in their bedrooms, very low key set ups.
Call to action: Make sure you have a clear call to action in your video so it's clear what you want viewers to do next.