SEO and knowledge are your best assets.
As
@Koala_Steamed said, this place is best used for getting knowledge while meeting new friends and colleagues. An audience, no matter the kind of video you produce or how much you advertise, is not going to be found here.
To gain viewers, you must manipulate YouTube's algorithms for SEO to your benefit, that involves understanding how it works and what makes the system tick. Use the knowledge of the system to better your video search results.
I cannot stress enough that advertising off YouTube is not going to help you whatsoever, you'd be wasting your time. Time you could've spent learning how to manipulate YouTube to your advantage.
To gain subscribers... Well, you don't. There is nothing you can do other than say "click subscribe" at the end of a video that would pressure someone any more than the quality of the content itself towards subscribing.
Make the content you make it and of your quality. To better the quality is to better the chance of someone subscribing, but only slightly. That's not saying quality=subscribers though. But the point is there is nothing you can do outside of the video itself to gain
faithful subscribers.