Your top #3 (FREE) ways to promote your Youtube videos

I'm sure this topic has been heavily discussed in the past, but, times change, and so does the effectiveness of marketing methods. I'm curious, what would be the top #3 (FREE) ways that YOU use to promote your Youtube videos right now?

Here are some of mine:

1. Leaving a link response in the comment section of non-directly related youtube videos - this means posting a generally valuable comment with your video link on other videos that are not directly in competition with your niche, but are tightly linked together - for example, linking to a nutrition video on a video that talks about stress management. For me, this turns out to have the highest approval rate, since right now authors of youtube videos have to manually approve your "link comment" for it to appear in the comments section.

2. Youtube SEO - analyzing, targeting and optimizing for easy to rank, micro keywords and shooting a lot of high quality videos, and at the end of each video you recommend your other videos to keep the funnel flowing.

3. Getting in touch with other youtubers which are at your level (but preferrably also not your direct competition) and arranging for a cross promotion - this can be a very good thing, but it all depends on how good your communication skills are. This can also lead to a fruitful relationship in the future.

P.S - You can also recommend a course or ebooks that you consider to be very good, as long as it's not shameless self promotion.