For me, to make web applications fast is to know the protocols that constitute the web, its a slow process but knowing networks "under the hood" will give you good basis and perspective to build upon when choosing frameworks or libraries to learn. I assume you mean the front end part of web development?well in my opinion you should learn from master craftsmen themselves ( those who designed the UI of popular websites), i mean, read their books and recommendations, know how to use their tools, know how they design things, know how to develop good taste. Good Luck!