When posting a video to YouTube,the description is so important. 
After all,YouTube is the second largest search engine in the world, so to be found in the search engines, we need to include a meaningful description.
Here are the things I suggest :
1 Firstly decide on your keywords.
This is a whole subject in itself, but let’s assume you have decided on
“How to make money online”
2 Include it in your title
However, it is better to make it more appealing, for example:
“How to make money online-learn the secrets never revealed before”
Or
“How to make money online-7 simple steps for you to follow”
3 I repeat the title as my first line of the description.
4 Include your URL in the second line including http.
For example, mine is
https://johnhayesonline.wordpress.com
The reason you want to do it this way is that the format above is a clickable link.
You do not want your viewers to have to copy and paste the URL, because most of them will not do it.
5 Write your description
Ideally this should be between 200 and 500 words.
The important thing is that you should write the description for the viewer NOT for the search engines.
When writing, keep the sentences short.
Use paragraphs with only 2-3 sentences per paragraph.
Your viewers will not read a full page of text with no breaks.
Use bullet points-these make the reading more interesting.
Try to include your keyword phrase 3-4 times in the description, but do not overdo it as it may appear unnatural to the search engines.
6 Include your other social media links
If you are on sites like Facebook, Twitter , LinkedIn, Pinterest, Google+ or any other of the major sites, you can show the viewer that you are active on other sites.
7 Include an external link
There are various thoughts on this, but it is something I normally do.
I normally include a link at the bottom of my description.
I go to google and type in the keyword phrase or something similar.
When I see the results I normally include a Wikipedia URL as this is a higher authority site.
I hope you find this useful, and if you have any suggestions or comments, please do not hesitate to contact me.
John Hayes
Online Marketing with John Hayes 