How to improve in chess 960

Then get better at normal chess - it's pretty much the same thing. But opening theory in normal chess won't matter in 960. 

A really good way is to understand and enjoy the basic principles of opening play in Chess studying their application in greater depth over time. There are a lot good books that cover the opening principals which don't not focus on memorizing. It has been realized by players like Nakamura and Svidler that all of the important priorities during the opening phase like controlling the center apply to Chess960 it just that the priorities are more flexible and contingent.

Chess openings can be a good way to learn Chess960 when the moves are all because of logical principals. There are a few cases when the opening theory in Chess starts to get so abstract that the reasons why an opening move are made are no longer because of principals, but because something has been found at a very deep depth that causes certain opening moves to need to be memorized rather than understood.