I think the best ways to promote your channel to get more views, subscribers is:
I found DM people on Twitter telling them to check out your Youtube or new video it is the best way so far it is working for me now i am getting a lot more videos views and subscribers than ever before.
1st you have set up a Auto DM(or multiple DM) on a site like Justunfollow.com each time you get a new follower on Twitter they get your auto DM saying thanks for following and telling them to check out your Youtube channel or video.
But you have to follow(a least +200/400 people at a time) lots of people(followers of Small/Big Youtubers and people who likes Youtube) after you set up a auto DM on Justunfollow.com
After over a month of doing DM people on Twitter I have a lot more video views and i was getting 1/2 MAX subs per month and not getting any video views, i use have only about 27/28 subscribers now i have over 60 subscribers on Youtube and most of them are active subs and i checked on Youtube analytics in the last month i gained over 30 subscribers.
My Youtube channel is growing a lot more now than over a month ago. :)
And it is NOTHING like Sub4sub because if you do Sub4sub all you get is dead Subscribers and is complete garbage.
OTHER GOOD WAYS:
Reply to your comments on your videos and post good and nice comments on other Youtubers videos and make friends and collab with other Youtubers.
Have a good/eye catching looking banner on your Youtube channel and create good custom video thumbnails on your videos because it attracts viewers and potential subscribers and keep posting good content on your videos.
And try to be consistent with your videos every week as it is not good uploading videos for a couple weeks and then after no new videos for a couple months because it puts off potential subscribers.
That all i have at the moment.
Hope this helps. :)