How do you approach (re)learning algorithms for code interview?

Learning or relearning ^^

I am curious to hear story about it, there is many company which do white-board interviews and ask some challenging algorithm problem in interview.

This is a goal that I never accomplished (to relearn algorithms properly), and to me it is hard to maintain the motivation when you actually never apply this learning.

Do you think it is a crucial learning ? If you did it, does it open more opportunities to you ?