Big arrows on the map are often misleading, and not always noticed, despite being big and arrows.
People just assume conquest when they see  flags and get frustrated when that doesnt work out well.
Or they keep trying to cap until they are rebuked harshly by some angry vet with an axe to grind.

Ingame chat messaging is hepful but time consuming.

EST:
Imperials cannot recapture any flags, they can only defend. Rebels have to take all the flags to win

(relatively simple so far, but we still get questions of 'why?' )

Flags have to be taken in order, look at the flags on the map.
Rebels have to take the ewok tree village before you can move to the wrecked speeder or imperial out post

(If we havent had a 'but, why?' yet, we'll likely get one here)

Ewok tree village can be captured out of sequence, before scout camp is captured

( This is almost never pointed out as by the time the rest has been explained the rebels will likely have steamrollered ahead and the imp new guys will be heading to ewok or scout to recapture it)

''Its over. Angel won.''   RSF Gurd

I'm totally willing to do voiceovers for that kind of stuff, be it in a silly way or not.