Er, advice? I'd start with rule changes before moving to tactics.
Let's see... stuff since the Gym sets... might want to start by mentioning new card types. Supporters, Stadiums (for the pre-Gym players), Tools (the people who played during Gym Heroes/Challenge might recognize Gold Berry as being similar), Pokemon-ex, Pokemon-*... can't think of any more offhand, but that's a start.
Other new stuff... I think there have been some changes for how Baby Pokemon work (the "baby flip" as it is often called), Pokemon Powers are now Poke-Powers and Poke-Bodies, and... uh... I'm too tired to think of more right now. But you get the point.
Also, it'd be a good idea to mention Delta Species Pokemon before any of you use or play against them. That could be quite confusing if they aren't prepared for them.
Yup. Rule changes first, then tactics. Always a good idea to complete the base before building a titanic skyscraper. ^_^