How can I write good responsive websites. Does it require much practice or there are some aids. Please help

Answer 1

if you don't use any frameworks/shortcuts, I think your website will be pretty responsive and light weight handcoded.

Answer 2

Practice. Understand design principles and UX design. Learn to use CSS flex box. You can practice finding very well designed responsive websites and try to copy them by looking at them. Copying for practice is not only ok but an excellent way to practice.