Hard work and dedication. Expect YouTube to be a marathon not a sprint. If you create 3 videos a week for two years you will have over 300 videos in two years that people can find bringing new views and potential subscribers to your channel. Make sure to try to learn from each video you create so you can use that knowledge to make the next one even better.
You need to learn SEO for people to be able to find your videos when they search. But even if you have done your homework and have 300 videos optimized for search that may not be enough by it self. A lot of niches are already very populated which will make it very hard for a new or small channel to compete. So you should try to find a less crowded niche or even a niche within a niche or a niche within a niche within a niche. It's better to show up in the top three spots for a keyword that only 100 people search for then to show up in place 162 for a keyword that 1 million people search for.
You should study the competitors inside your niche, what do they do better than you? It can be everything from quality of video/audio to editing, to the way they speak, to personality, to storytelling, to humor and so on. What can you learn from that information and how can you use it to improve your own content? What videos are doing well for your competitor? Can you do something similar?
Have people study your videos and give you feedback, you don't want to get feedback from "yes-sayers" you wand feedback from people who can actually give you constructive criticism.
Study your analytics and learn from them. Is any of the content doing better or worse then the rest of your content? Can you stop doing the content that are doing worse and can you create more of the content that's doing better? Do you have a high or a low audience retention? If it's high you are probably doing good content but people don't find it (seo, your niche, marketing etc). If you have a very low audience retention your content are probably one or multiple of the following: bad, worse than your competitors, boring, you use click bait (people click becuse of you thumbnail or a title that making believing that your content is one thing but it's actually something else. You can also study the adience retention for individual videos and try to find out why they stop, like if you are getting a big drop off after 20 seconds, what happen around that time in the video? Could you have done something else to keep them interested? Getting a good audience retention is something most YouTubers struggle with.
Expect YouTube success to take a long time, always try to learn and improve and don't do it if you don't enjoy it.