The answer is cannot be answered in one word, and there is no one solution. There are so many different ways to get more subscribers (read here), and these ways depend on the strategy you are following.
One strategy would be to ensure that your channel comes up during a related search. For this, you have to ensure that your content is SEO optimized. There are two ways of going about it; first, you make a youtube (check here) channel description, where you mention who you are, what your channel (get more info) does, how your channel is going to help or entertain the viewers, why they should subscribe (more details) to your channel, how often they should expect you to post new videos and such questions.
Second, you should make a compelling video description. Keep it long, but not too long, a few simple short sentences, so that search engines know that your particular video (finding out more) caters to the preference of the audience. Experts also say that if your Youtube (visit here) video is longer than ten minutes it is more likely to pop up in a search result.
The other strategy is to ensure that the people who watch your videos subscribe (for more) to your channel, and watch more videos. The most important thing is to have a channel trailer, about 60 seconds long that could include clips from your most-watched videos (get to know more), or your best content, also talk about who you are what you do, and why you are making the content.
To ensure that the people who watch your video subscribe (for more information) to it, be sure to have a strong CTA (Call To Action), i.e. tell them exactly what to do, ask them to subscribe (further details) to your channel, press the notification icon, and tag a link for another of your videos to make sure that they watch more of your content. Also, always have the subscription watermark in your videos (additional information). Having catchy video titles also helps, along with having graphics text, change of video angles, or other images and clips to break the monotony of the video, this is called pattern inhibition.
The final strategy would be to grow and keep the Youtube subscribers (know more) you already have. For this, the most important thing is to focus on the quality of the videos. If your fans like one particular type of content, give them more of their content. Make the videos that your fans would like to see, not the ones that you would want to make.
Also, work on the channel logo, and have a tagline that shows your USP (Unique Selling Point). Whenever you can, reply to as many of the comments as possible, and if you like a comment, be sure to give it a creator's heart.
There are many other simple hacks, the tips and tricks of the trade to increase your influence and get more Youtube subscribers (find out more). You can also buy Youtube subscribers (find more information). Making abusive content or using downgraded language may get you more watch time, but it will fail your very purpose of making quality content.