well first off (I know a lot of growth experts say to do this, but it irks me) DON'T ask for someone to subscribe within the very first seconds of your video, there's nothing I hate more (luckily it's died down) than a video that starts off with "please subscribe" or the annoying "but first, let's get this video to 1000 likes"
Davey504 is about the only person who can get away with it, but he does it with such a dry sarcastic comedic style that it works.
If you can do your call for subscribing in a creative clever way, then sure... but you're best getting right to the content, and adding in a short "if you want to see more content like this, be sure to subscribe" bring the value first so people KNOW why they're subscribing.
Outside of that, find your Niche (your topic/passion) for me it was dinosaurs and drawing. So I focused all my efforts on drawing dinosaurs. It didn't take long for dinosaur fans to find my videos and subscribe. They knew what they were getting, and within a few months, I had 1000 subscribers.
I'd always focus on the content, not the number. There are of course tactics for better growth, just like there are tactics for sales and conversion growth... but your audience don't care about your goals, they just want what they came for, information or entertainment. Provide that, remind them to subscribe for more, and the rest is up to the audience to decide if they want to hit subscribe.