I would recommend LeetCode, doing problems on a white board, and buying a book called "Cracking the Code Interview." I also highly recommend creating a GitHub account and proving you can work well with others with the same toolchain that is used in production in most places.
I am already pursuing what you have said(my leetcode skill is not good enough but i am atleast on correct path). I am Open Source contributer and have done many projects and contributed to few other projects.
