The best way would be to get strong backlinks to the video, depending on the competition though. Take the websites on the first page of the keyword you want to rank for and analyze them. It's really unnecessary to create 1000 backlinks if your competitors only have 5 links, so how many backlinks you need will depend on how strong your competition is.
But it's much easier to rank a video with backlinks and most of the time you don't need tons of backlinks, just a few strong ones will do.
Getting authority youtube accounts to feature your channel on theirs will also help improve rankings. Also leave a comment in the discussion area of authority channels. Hope that helps.