Answer 1

Create your own imagination and try to turn it into code
This is the best way to improve.

For help you can Vist site like
W3schools
Tutorial point
Geeks for Geeks
Stack overflow
Programing simplified
And of course sololearn discussion form

Answer 2

practice. learn to optomize. about all I can give with no specifics

Answer 3

i practice my js on jsbin.com. to challenge yourself id suggest codewars.com