From a technical perspective: Master at least 2 different paradigms (for example object-oriented and functional) and 2 different programming languages (for example Java and JavaScript). Why? When you learn to code, you usually start with one language. You are able to write application that will work, but you are somewhat limited. By learning multiple languages you can compare how things can be achieved. You learn the concepts and when you do that, you can pick other languages more easily.

From a non-technical perspective: Learn how to explain difficult things in a simple way. Why? Because most of your time you will be either teaching junior developers or talk with stakeholders and both of these groups have limited technical knowledge. You should prepare for lot of questions and lots of misunderstanding. If you have practice on your own children or try the "Explain like I'm five" channel here on dev.to :)