I looked at the metadata for your video "Which Comes First Aerobics Or Weights?" and one of the first things that I noticed was that your description is basically just a laundry list of tags.
"In this video I will be talking about which comes first aerobics or weights, cardio workout, cardio exercise, cardio and weight training, cardio after weights, cardio for weight loss, cardio weight loss, cardio before weights, cardio after lifting, cardio strength, cardio to lose weight, weights before cardio, cardio strength training, cardio after weight training, cardio and weights, cardio and strength training. Cardio before weights. Cardio after weights."
This is baaaad. It's not human-readable, and in fact, it clearly reads like someone trying to game the system. But secondly, rather than focusing on any one key phrase, it tries to address a ton of key phrases, and so it's dilutes the significance of any of them.
I think that you want to pick a central keyword/phrase and then focus on that. Think about one term that really addresses the subject of your video that people would actually search for, but that isn't overcrowded by so many other videos (here is probably your challenge -- there are already a LOT of fitness videos. So how do you distinguish from the others???)
So, in this case, I would start with your title. Are people searching for the phrase: "what comes first aerobics or weights?" No, not really. (Try typing that in. Does it ever come up as an autosuggestion???)
OK, maybe that's too specific. Maybe just focus on whether people are searching for "aerobics or weights"
If I type "aerobics" in youtube search, there are lots of autosuggestions, but so far, nothing comparing/contrasting to weights. So, I type in "aerobics or"...Again, there's nothing comparing/contrasting to weights, and in fact, the autosuggestions that youtube suggests aren't really about using the word "or" at all (there's some alphabet aerobics original, which is clearly not what you want.)
So, right of the bat, this suggests that your title is not optimized around what people are actually searching for. So, maybe "aerobics" isn't what you should lead with. What's a different possibility? Maybe cardio? So, I start typing "cardio" in youtube search. There are lots of autosuggestions, but so far, nothing about comparing/contrasting to weights. So I type in "cardio b". "Cardio before or after weights" is something like the 7th autosuggestion...not bad. for "cardio be", it's the top suggestion. But if I do "cardio v" then "cardio vs weight training for fat loss" is the top suggested search, and that's a pretty specific "long-tail" keyword. If either of these are applicable to your video, I would consider optimizing around *these* sorts of phrases, rather than "aerobics or weights".
Optimizing the title comes first. You have to pick your specific focus with the title first. (If you start looking at search results, you'll see that youtube *typically* prioritizes exact matches in titles first.) (That being said, youtube ultimately cares about watch time, so if a video with a totally different title can generate more watch time for a given search, then youtube will rank that higher, even if the title/description/tags don't seem to "match")
From there, go into your description. Your description should be human readable -- so it should be key phrases incorporated into readable sentences and paragraphs. Lists are not viewed as "human readable". And again, with key phrases, you should try to focus on a very narrow range. The thing that I'm seeing with your choice of phrases is that you are using a bit of a shotgun approach -- you want to appeal both to the idea of "cardio before weights" AND "cardio workout" AND "cardio exercise" AND "cardio weight loss" AND etc., etc., etc., But you have to ask yourself -- is this video really about comparing and contrasting the timing of cardio vs weights, or is it about specific cardio exercises? Is it about cardio for weight loss or is it about comparing the timing of cardio vs weights? Pick a focus and then develop a description and title around that focus.
But even when you do that, your description should be human readable sentences, preferably with the first 3 sentences being the most relevant. Currently, your first sentence of your description is a link to a survey and a request for people to fill out that survey -- so that's not a very effective use of descriptions. Please note that the first few lines of a description show up in youtube search, and again, you can tell that exact matches are "bolded" by youtube, to highlight that youtube took that into consideration in a particular search query. So, if the first few lines of your description are links to a survey, then there's no search term agreement for youtube to "bold".
Now, to end all of this I want to mention something I said a few paragraphs back. ULTIMATELY, youtube cares about watch time. So, all things equal, a video that drives more watch time will be ranked higher than one that doesn't. However, I think that what youtube does is that it gives every video a probationary period -- for the first few days, youtube still tries to figure out what the rankings should be, so it gives a temporary boost to new videos based on SEO. So getting SEO right is critical for those first few days, but if the first viewers don't stick around, then youtube will then say, "Oh, well, this video doesn't generate watch time, so maybe it shouldn't be rated highly."
