There are 3 main ways to use YouTube for promoting whatever it is that you want to promote. The first I would like to tell you about is the use of supportive video. Lets face it almost everyone would like to get information via a video if possible. This is where you need to make a video that sells yourself or your company. It is an introdution more or less of who you are and why people need to follow you and watch your videos. This is not a video that is meant to go viral. It is an informative video.
The second way is to use Search Discovery or SEO Use of Video. Believe it or not, YouTube is the second biggest search engine only behind Google. What you want to do here is make a how to video that relates to the product or service you are selling. By using a how to video you can put links into the video that takes the viewer to your website. Lets say you sell homemade beer making products. You would make a how to video on making beer with links to your website selling the products need to make the beer. That is just one example, but I am sure you get the idea.
The third is external promotion. You need to get as many views as possible so your video will come up when people do a search. You do this by promoting your video on your Facebook, linkedin, twitter etc. You should also email your video to your email link. Get it out to as many people as you can so they will view it. This will drive your video to the top of the search.