TL; DR of this: Tags should be second, the video topic should be first.
Tags and SEO are the most complex part about anything related to the Internet.
If you want to rank on a search term you pretty much need to be in the right place at the right time. If you make a series of something that hasn't just started to pick up a huge trend you can forget about ranking on tags.
Let's take a look at how you can determine what tags to use:
We'll start off by finding out how popular a specific tag is. You can do that using two metrics: SEARCH VOLUME and COMPETITION.
Search volume is how many people search it and Competition is how many people make videos about it.
Time to explain how to work with these numbers using boring ECONOMICS! WOO EDUCATION!
In this graph (Source Wikipedia) we see Demand and Supply. In our case Search volume is the demand and competition is the supply. Why did I choose this boring example? If there is demand there needs to be supply. Supply creates competition. To have a working product you need to find a niche. Something people want to see but can't see yet because there isn't enough out there yet, regardless whether they know they want it yet. If you can be among the first people to make a video on a topic that will be trending you've won.
Let's get to a practical example: My terrible channel back when I used to make videos.
My videos were ghosting around 10-40 Views. Then one day a Minecraft Server created a new Anticheat. I got online, recorded someone cheating and getting banned. I slapped on the most cringeworthy title and included the server's name and the name of that anticheat. [Hindsight: The tags I used were terrible defaults but it was the title that gave it exposure] That video did amazingly well:
After that I thought about what I'd done correctly and all I found out was that I was at the right place at the right time. I made a video rank on the front page (It was second on YouTube search, now slided to like 11 but hey, still front page) of a topic a lot of people were going to search about and a lot of larger YouTubers would later make videos about.
This is what no extension can help you with. You need to find a topic people will be interested in that you can make a video about. The video can be edited together in 2 hours, it doesn't need to be a masterpiece, I'm showing you stats of a Minecraft video barely scrapping together 20 FPS here.
If your content doesn't rank however you tag it chances are it's just saturated and there's really nothing you can do about that. If you want to keep making videos about it go for it but don't expect YouTube search and recommendations to help you. There are just some topics which you can turn and flip however you want without them making it onto a search results page. Simple case of "
you can't polish a turd".
What you need to look at is what people will be interested in tomorrow. What people will be interested in next month. Yes, that's forecasting the future in some regard but it's what separates a discoverable channel from everyone else. Give people what they want tomorrow, not what they have today.
