Hey Sumi, this is a very common question, so I am going to suggest you view some of the recent threads on this topic. That said, remember there are three things you can always improve:
- Content - audio, editing, lighting, storyline, your voice and presentation
- Thumbnails - how do they compete against the other channels you compete with? How do they compare with other videos returned with your keyword?
- SEO - are you constantly improving your SEO?