I haven't taught my kid to ride yet because I started him on skis first, so I can't give any technical advice, but just some general stuff.
The biggest thing is to just make it fun and add some stuff to the experience that makes it fun besides just riding (i.e. hot chocolate afterwards or a mini snowball fight as a break).
When my son first started on skis at 3 he enjoyed it but lost interest pretty quick when he got tired. Part of me wanted to convince him to keep going since we made the trip up to the mountain, but it was better to not push it and just ensure he enjoyed his time at the mountain even if he didn't ski a ton at first.
If you can, get a little video of him riding. My son loved, and still loves, seeing videos of him on the hill. It's good to reinforce how much fun he had and motivate him for the next time.
That's all I got. Have fun and good luck!
Thanks Schmitty, Those are great suggestions. Definitely bringing the video camera and the helmet cam.