To me the best self promotion is not self promotion at all. Basically what I mean is, you should go to other people's channels that are larger than your own but not TOO much larger, and try to befriend them, let them know you like what they do. Ask them if they have any tips for you. See if they wanna collab with you and just be available and real and nice. The WORST self promotion, the stuff channels do that make me want to burn their channel to the ground, is the copy paste messages that lie to people and tell them they watched when they didn't or act like they're a fan when they're not tagged with a "You should check me out I bet you'll love my stuff!!" This is a great way to get other vloggers to hate you LOL
And if you must kind of "spam" people, at the very least be up front about it. Just say "Hi I am a new channel and have trouble getting views could you take a look at my stuff?" Or go to a big channel and comment "Hi I'd really appreciate anyone reading this to take a look at my channel thank you" I don't encourage either of those things, but it's 10 times better than telling me "man your videos are awesome! I'm a big fan! You should check me out I make minecraft videos!" Yet I gained no sub, yet you didn't comment on my videos, that is a way to guarantee I will not only not watch your video, I'll mark you as spam.