In one of the Facebook groups I frequent, a user asked
“Who’s great at building YouTube channels and does not mind offering some free advice?”
A little of what I contributed:
Build your channel around a clearly defined (as defined by search algorithm) subject – with inherently related keywords / phrases that are recognised by Google (and YouTube, by proxy). This might sound odd, but for example you could be developing an audience for Video Games – YouTube will not tightly-associate ‘video games’ with ‘top 10 bosses’ – yet the 2 are very related. https://keywordtool.io/youtube will help as it’s YouTube-context-sensitive.
Brand your channel – not just the cover photo, but the style in which you format descriptions, your video thumbnails, the channel watermark – consistency will breed trust and some degree of authority.
Actively purse action-taking: remind viewers to subscribe, and remind them so more – same for enabling notification. Ask them to hit thumbs up.
Comment on other YouTube videos with funny/useful/interesting content – make an excuse to link to your own video where possible; this can be appreciated by users and the original creator, depending on what you link to, and how much it bolsters the authority of the video.
Engage your users; reply to comments, Like their comments.
Promote your videos on social media; this is very easy – right from within YouTube; personally I use Zapier + WordPress to create more substantial impact around the key word/phrase – as well as linking.
Determine why people should subscribe … sell yourself on why, so that you can sell the reason to others.
If you link to your YouTube channel from anywhere – append a subscribe parameter so that when they visit your channel, it automatically pops up the Subscribe box.
Examine cost-per-click data to inform your decision making on the feasibility of a video title / tags – research alternatives / long-trails.
Spend time fully configuring the meta-data for your content – genre, location, subject matter, CC if you have them.
There will be much more, much better advice out there but I hope that helps at least a little!