It has a few aspects, such as;
- Title
- Thumbnail
- SEO
Your title needs to be click worthy. Don't call something 'Vlog 2 in Paris', but take the most outstanding thing you did and maybe call it 'Best view from the Eiffeltower!'. Same goes for gaming content, don't call something 'PUBG part 4', but again pick something cool or funny that happened and put this in the title. People will get curious and click the video.
Big part of clicking the video is also the thumbnail. It needs to show what it is about, with either a short, big text on it or none. Thumbnails are small, so don't overcrowd it with text. If you're a vlogger or facecam gamer, it is advisable to put your face in the thumbnail, preferably with an expression that links to the title and subject of the video.
Last part I put in is SEO (Search Engine Optimisation). This isn't something that makes people click your video, but something that makes them FIND them. Big part of SEO is knowing what people are searching for and which terms are relatable to the subject and content of your video.
More information on all these subjects can be found in the forums, just have a look around
