Stop trying to "hack the system" with 1 video you are hoping will go viral. It won't work. Instead, make lots of different videos and see which ones become popular.
There are lots of websites claiming that there are "hidden tricks" to promote your video, but none of those hidden tricks will work if your video is horrible and nobody likes it. The solution is to make lots of videos, see which ones are popular, and then improve upon the videos that are successful.
Great Videos = More Free Promotion from viewers.
So called "youtube hacks" are actually just little known features that everyone can use, and often do use, so they're not really hacks at all. They're just common knowledge and some people don't always use them. That is not a hack. That is just a person who doesn't follow common sense.
#2. Follow an Upload Schedule
Another thing to be doing is to be making 4 videos per month (or more) and be uploading 1 video per week. Fulfilling that minimum shows that you are more serious about video production and YouTube's algorithms treats you as such.
Thus if you are already following tip #1 above and making lots of content, releasing your videos once per week (eg. every Saturday morning) then following #2 is done easily by scheduling your videos to become available 9 AM every Saturday.
This is known as the "1x4 Schedule". One video for 4 weeks, every month.
If you were somehow producing lots of videos you could just do videos every day (and have no life), but one video per week is easier to do as it allows you to still have a job, a life, a love life, etc.
Regular Frequency = Important.
#3. Stop thinking about making videos, and just make videos.
If you have the time and a basic idea, just make a video.
Don't overthink it. Just make it and see what happens.
Procrastination is the death of ideas that never get made.
#4. Keep the Intro Short but Sweet
Don't bore people with the first 8 seconds of your video. That is when people are most likely to click pause and stop watching.
You don't need a long intro with music on every video. Leave that at the end. The very start of the video should be kept short but awesome.
Also if possible, don't even include music in the intro. That just annoys people. Just show a logo for 1 second or less and go straight into the awesome content.
#5. Make Playlists
People are more likely to subscribe if you have playlists. So organize all your videos into playlists so that there are different themes.
#6. Promote on Social Media
Don't bother with anything else. Those are the Big Three.
If you want to go a step further use reddit and subreddits too. Instagram is okay, but not the greatest for promoting youtube videos as Instagram has its own video upload service.
#7. Create a website / blog
Promote your videos and written pieces on a website / blog, where you can embed your videos and gain more subscribers to both your blog and your channel.
#8. Use Titles that are easy to search for
Choose a title that makes it easy for people to find your video a 2nd time, so they can watch it again, is easy to remember, and sounds awesome. Avoid generic sounding titles.
#9. Translate your most popular videos
Okay, so this is a tip to do when you've already hit the jackpot with a popular viral video.
Take the time and create translations of your best video(s) into other languages so that they can be more easily promoted to people who speak various popular languages. eg. Spanish, French, Japanese, Korean, Chinese. Depending on the topic you may want to add specific languages you feel are important.
It is possible to add subtitles to all your videos, but this is time consuming and really only worth it when you have a video that is already super popular.
#10. Invest in better equipment, editing software, and better filmography skills
Having better camera equipment, software that allows you to make better videos, and learning how to do different filmography tasks allows you to create a broader range of things in your videos.
eg. Time lapse videos are great for showing a long task which would be boring to watch the whole thing slowly, but is more enjoyable when it is sped up to an almost comical speed.
BONUS TIPS FOR BOOSTING POPULARITY
Updated August 2019.
#1. Giveaways and prizes may help to boost subscribers and comments, but you are really just paying for subscribers. If your videos are good and worth watching then you will gain subscribers anyway. So save your money and focus on making great videos.
#2.
Aim to make videos between 10 to 16 minutes long. According to my
research that is the Goldilocks Zone in terms of making popular videos.
You can make shorter or longer videos for the sake of variety, but if
you want videos to be popular aim for 10 to 16.
#3.
Original Content. Borrowing videos from other sources and commenting on
the content is so 2011. Since then YouTube has changed algorythms
multiple times so that commentary videos are less likely to be shown to
random users.
#4. Content
that Endures. If a video is about an old news topic it won't be fresh
or popular years later. Instead, a video that always feels fresh on a
topic that hasn't changed in years, eg. Woodworking, fishing, how to
videos, etc, will always be relevant and endure. YouTube had updated
their algorythm is recent years to put more emphasis on YouTube channels
with content that endures.