in which you used to live
when you followed the ways of this world
and of the ruler of the kingdom of the air,
the spirit who is now at work in those who are disobedient.
The word "ways" refers to a manner of life, your philosophy, so to speak. We all used to follow the philosophies of this world. We have all believed in this world's teachings. We have believed such lies as, it isn't really that bad or I can repent later. But those things are not true.
And those lies come from the father of all lies, the devil himself. He is the ruler of the kingdom of the air.
And take special note: whether we like to think this way or not, he is at work in those who are disobedient.