In one line, I would say that the successful channels bring *clarity to a desirable topic.*
There is a lot more of a focus on scripting, and planning for the video than you realise, with channels like PewDiePie (60 million subs) actually being on the very low end of production quality.
I would take these action steps:
Study 3-5 channels in your niche. The channels you use should have large subscriber to views ratios. For example, you want the channels with 400 subs that have 2 million views, as opposed to the channels with 200k subs and 2 million views.
Once you find those high performing channels, take notes on their videos about what recurring principles stood out to you in their content. You might need to watch a few videos on each channel, but you will start noticing patterns very quickly.
Write a test video script with 400 words (three minutes of content). Use the software Boords to plan out what visuals might be best suited to each line of dialogue.
Then use an easy editor like Kapwing to edit your content. You can make seriously good content using stock footage, text and filming yourself speaking (if you're comfortable).
Ask for feedback on designernews or reddit (pick the right sub reddit). Use that feedback to develop a second video, and then repeat the process.
This whole time, you should be using Vimeo's analytics to track viewer engagement. If you are in the range of 60%+ for your first 5 videos, that is pretty excellent.
Anything lower than 20% needs serious rethinking on tone and introduction.
We wrote on some more trends in video that might be of use to you here: https://vidico.com/news/video-production-3-trends-for-2019-that-you-should-know/