Wow, you really sound annoyed CoolMoo5
The best way how to do self promotion is like in the advertisement.
The best advertisement is the advertisement you don't even realize that it is advertisement.
If you write "Watch my awesome new video!!!!" everyone will be annoyed.
But if you write funny or intelligent comments, people will have a good view on you and will more probably check out your channel.
I for example sometimes go through many video dslr tutorials and answer all the technical questions people have, which the big youtubers are to busy to answer. I can't give numbers but I can imagine very well that this draws good attention to my channel and the whole community benefits from it.