How to become a good python coder ? Should I start with python 2 or python 3 ?

Answer 1

Finish a course on Solo, then do the Python for Everybody on coursera.org. Then practice a lot.
Py2 vs Py3:
https://www.sololearn.com/Discuss/277314/?ref=app

Answer 2

You should use 3, unless you have a good reason to use 2.

I would not call myself proficient at python yet, but I can give you some advice:
1. Learn to use generators, decorators and list comprehensions.
2. Familiarise yourself with the built in functions, especially the ones, which are a little more "functional" in nature.
3. Become a good programmer in general. If you have all the paradigms python supports down and can integrate them, your code will improve.

I also recommend to study some theoretical computer science and mathematics, as this will give you the tools to solve challenging problems.