My son and I ran the first mission of the campaign last night. He as the rebels won the mission and was awarded "A New Threat" story mission. Per the instructions he also drew two side mission cards. I am confused as how to choose the next mission. According to the rules and reference guide you can't choose any side missions if there is an open story mission. How will you ever be able to run a side mission if there will likely always be active story missions? Thanks!

Oops wrong forum. I'll post in the campaign forum.

If you look at the back of the campaign guide or in the download section of imperial assault there is the campaign log, which shows the order of the missions. So after Aftermath, the first story mission, follows a side mission which will be chosen from the two drawn side missions. After the side mission you draw another side mission so there are always at least two side mission. Then a story mission as per log (that would be a new threat) and so on.