I'm good. 30+ years of experience, all levels, all subjects. Can make the stuff easy to understand and remember. And make it relevant and interesting.
I try to keep communication open with all schools and the teachers. For example, two days ago, I had a 5th grade. The assignment was to write about what makes you unique. I saw a boy who wasn't doing the work. Instead of coming down on him, I struck up a conversation, asking him if he would prefer to make a list of all the wonderful things about himself. He looked straight ahead. I then asked to tell me just one really good thing about himself, at which point, he began to weep. For a fifth grade boy to be so upset as to cry was noteworthy. I excused him from the assignment and got him onto something else to do. I shared this with his regular teacher who was in the school. She explained that this boy had issues from feeling inadequate and self-loathing. She and the social service people were already on this.
My point: What if this wasn't already known and he was flying under the radar? A substitute can notice things that may not be noticed by the regular teacher (or can confirm what's already known). You aren't a placeholder. You don't do drive-by teaching. You make a difference, if only for one day.
I've had good days and bad days, but I still return.