That is a great start. I'm in a similar position to you and all of the job interviews I have come up against will require whiteboarding / coding tests.

I would recommend to starting something like Cracking the Code Interview on Hacker Rank and begin working through the problems.

https://www.hackerrank.com/domains/tutorials/cracking-the-co... (will have to create a login I believe).

I would also recommend not using any external libraries, even basic stuff like collections for Python. I was not allowed to use anything in the coding tests, only standard libraries.