To be an expert
1. There is a saying without creating proper foundation a building cannot be made. Once a base is apt, then a web developer can move ahead. For professional web developers, it may sound odd that there is no need to go back to the foundation, but there is. They will realize it when they do it. There are numerous points which may have forgotten by them or a few points may exists which they thought are of no use at that time. So time to time brushing up is a necessity.
3. While working on the browser, it is a must to consider the operating system a web developer is working on. There are many ways to find it, and he can learn those techniques and employ them appropriately.
This is not a final step neither expertise can be taught to anybody. If you are a professional web developer or want to be the one, then you need to take the initiative. You have to be ready to work hard but in a smart way. You require fighting with difficulties which will definitely go long way with success.