For me personally, one of the pieces of the game that really makes the learning curve steep is how activation advantage and initiative work out with each other. This is where trying to teach someone how to play is also difficult- it's a really odd concept that an 18 point rebel transport can be so valuable for nothing other than what is equivalent to a "pass."
Coming from the WotC SWMiniatures game, this was one of the easiest concepts for me. That game made strong use of very similar mechanics, and even had options that specifically played around with it (like characters that gave you even better activation control, and characters - Thrawn! - that gave you greater control over initiative).
