I know this probably is going to be futile, but I have my reading order like this:
Secret Wars #0
Secret Wars #1
Secret Wars #2
Where Monsters Dwell #1. (Shows effect of Last Incursion on The Far East Earth), or
MODOK Assassin #1. (The first story page gives the first thorough look into Doom and origins of Battleworld)
After those last two, you could read anything, but I like the refreshing intro to A-Force and Arcadia, so that is my 3rd alternative for after SW#2. (Ultimate End #1 also has an Incursion anomaly like Where Monsters Dwell. MODOK could as well, with that Asteroid shower).
So after SW#2, what book should be the one that gives the best lead into Battleworld?
It should be noted, 616 and 1610 Manhattan was incoming at the Last Incursion as region 20, so regions directly around it (Doomstadt, Higher Avalon, the City and Doomgard) should have registered its arrival in a big way.