I don't think you can get people to share your video unless they want to, I'll ask viewers at the end of the video to like, comment or subscribe if they enjoyed it. For SEO I try to use a combination of keywords that will be highly searched and more specific terms. So If it's for a video game I'll use: [Game] Gameplay, [Game] Walkthrough, [Game] Playthrough and If it's for a specific level or boss I'll use: [Game] Level 1 [Game] Fire Boss, etc.