Learning how to think systemically is a matter of capacity development. There is knowledge to be acquired, skills to be gained and opportunities to be sought to apply the knowledge and skills. Where do you start? Generally speaking the best choice is to start where you are right now. For instance, do the notions of focusing on inter-relationships, perspectives and boundaries help you improve your own understanding of capacity development? If they do, then start there. If that is insufficient, then dive a little deeper, pick a systems method or approach that seems promising for a particular issue you are engaged in.
Capacity.org: A gateway for capacity development has a number of articles about thinking systematically. This article outlines the history of three systems concepts: inter-relationships, perspectives and boundaries; and how understanding these support capacity development.