Thanks for the tips. We will try to emulate this strategy. With out giving away your trade secrets, how did you go about optimizing?
There are really no secrets as such. Just lots of hard work and lots of analysis and testing.
Study the fellow youtubers in your niche, taking note of their tags and descriptions. Go one step further and ensure you encompass all their tags and variations in your description. this goes back tot he old days of google and trying to get your blog ranked on the first page of search.
For tags, type into the YT search bar your tag/keyword then scroll through the alphabet to ensure you capture all possible search terms. Ex: "keyword a" "keyword b" ... "keyword z". Use everything suggested by YT that's relevant to your video as that's the raw search terms that viewers are searching for. Incorporate everything into your description and pick the most pertinent (highest search low competition) for your title and first few lines of description (Tubebuddy helps here with tag rankings).
Other things about optimizing your videos and time spent is study your niche and what's on offer already, not only in metadata but as a whole picture. Look for what's popular. Looks for trends and ideas they are following. YT recommends in many courses in the Creator Academy to create videos along popular topics and take advantage of key note events. Try to get onto the trends and hot topics in your niche.
For kids/toys channels last year it was giant surprise eggs, and several channels blew up to half a million+ subs on the giant eggs. The last few months it's "superheroes in real life" and such. That's what the algorithm (viewers) is hungry for, if you feed it what it wants it'll spit out your videos into search and suggested.
But it's a long involved process to get a feel for what works. If you see something work on your channel grab hold of it and feed more of the same into the algorithm. If you study carefully the releases of some channels and cross-reference in social-blade you can see the paths to growth that other channels had taken.
That's all just a start. There's so much more stuff here and there along the way.