Regardless of what constitutes a good teacher there are signs to look for when you are learning how to teach that let you know that you can actually teach, in the institutional sense, that is. These are not things that other people tell you you are doing but things that come from within. There's something quite unique about teaching; it's the only job where you are face to face, within one room, and in control of up to 30 other people for around 180 days a year. This is what sets teaching, in the institutional sense, apart from all other human endeavors. So knowing, for yourself, that you can do it is a huge milestone on one's life. This "knowing" usually occurs in an instance, in a trice, momentarily; it's not something that creeps up on most people.
I knew I could teach when I was called from my class one day to deal with an urgent issue to find, when I returned, some 7 minutes later, all 34 fourth graders were still happily working on their individual assignments. Last semester I finally saw it happen with Teal, one of my student teachers when she stopped during a class and said quietly "you're all being so good". Yes, I know that teaching is infinitely more than classroom management but that institutional sense of teaching comes primarily from that threshold of confidence across which all successful teachers step at some point.
Then begins the life journey of learning how to teach in the pedagogical sense where the learning of each individual student in your class becomes the number one priority and your knowledge and understanding of the subject matter enables you to optimize the learning of each of these individual students. OK, so this is how I define good teaching!