Not only is this one of the most frequently asked and answered questions, you are literally the third person to ask the same exact question in under 12 hours. I suggest you read the dozens of other threads where this question has been asked and answered.
Just focus on SEO, thumbnails and I would recommend using TubeBuddy since it has a inbuilt checklist as a starting point for having a well optimized video.
Also I would recommend watching tutorials and as @SILTHW said reading a few other threads along with finding what works for you as there is no cookie cutter for gaining subscribers.
Making out your good content, targeting the type of content your audience are much into it, and then begin to work towards it and use call-to-action in most content and give them a reason for them to sub your channel. That's all.