There is no doubt that as teachers we are always learning. I suspect a good teacher should be learning just as much as their students do.
I learnt today that the complex session I taught on CSS went fantastically well, because I was primed and ready for it.
The 'easier' session I did on optimising graphics for my later group was somewhat less successful. It lacked clarity from the outset, because I had spent so much time concentrating on my more difficult session for the day.
So, next session, I'm going to approach the same task as a puzzle - here are my images (a bmp, a photo with a huge file size, and a photo that is simply too large in its dimensions) and get my learners to add them to a website. This will force them to solve the same issues, but in a more practical way than just 'optimise these images'. I think that will get them to see the reasoning behind the session.
On a plus note, we made great use of LAN school as a way of demonstrating a very well thought out response to the task by one learner.