When you get new subscribers, talk to them. Interact with them. Let them know that you are interested in checking out their channels too, but not only on YouTube. Interact with the people at YTtalk more often. You don't have to ask them to take a look at your channel directly/indirectly, but if you pique their interest, they'll automatically get curious and see what you're all about. If your content excites them, then you'll earn another new subscriber.

Learnt this from my awesome sauce pocket master,
symphonious7
The best tips I've got to give you? Be a YouTuber who's out for passion, not for the money. Yes, a little money is alright. But, let that come later when you're bigger. People will notice your drive and will automatically follow you.
My last tip: become a genuine member of YTtalk. Most of you probably don't know, but I learnt so much from YTtalk. I've gained over 100+ subs since I joined the forums in less than 3 weeks. 100 subs may not be much to most bigger YouTubers at YTtalk, but it is definitely an achievement for me. This motivates me to keep doing what I LOVE doing. The key factors are interacting with forum members & allowing your passion to keep you going as your channel gets bigger throughout the years.
That's all I have to say for now. Hope this helps!