SEO is the most important element of YouTube Marketing. The better the SEO, the better would be the search results.
Title: Write title for the video within 50-65 characters. You can write up to 100 characters, but the search will opt up to 65 characters. Write the title relevant to the video.
Description: Write down the complete description related to the video. Try to add some long keywords or long tail keywords in the description.
Tags: Write down tags or keywords relevant to the video. You can add up to 20 tags separated with commas.
Comments: Having interactive comment sessions with the users/subscribers can help your video to get good SEO score and know the feedback of your users. Check the comments what you receive for your videos, and moderate those if required. Even you can turn off the comment box also.
Likes & Dislikes: Having good number of likes is good for SEO video. It will make an interactive session between you and your users.
Subscribers: The better the subscriber numbers, the better would be your video ranking on YouTube. Good Subscribers base helps the video to have authenticity in YouTube. So it is better to promote or ask your viewers to subscribe your channel for more updates.