The way I see it is that you have to make a video which is "Trending" at the moment but is relevant to your audience. With this in mind, you have to find a "KeyPhrase" which is directly linked to the video that you're making.
For Example:
If it's a horror game, that's popular, find a "KeyPhrase" which is relevant but hasn't got much competition i.e. The title of the game.
Enter the title of your video you're about to make into your search engine on YouTube, and you'll see how many search results the video you're making will have.
Basically, you want to have a Title with low competition but a high search volume. This is so that your video is more likely to show up on the first page.
I hope that this has helped if you have any questions just ask