There are as many valid answers to this question as there are trainers.
For me, the thing that makes me a good trainer is that I have a mission statement for what my fitness gifts are. Every class, every client, every workout I plan fits within that mission. This consistency lets people get to know who I am, how I approach training, and what my approach can do for them.
I don’t teach a class unless I love it. I don’t train a client unless I like them and feel like I can help them. In this way, we bring the best out of each other.