consider that losses are going to be much higher than in CBT. AS chaos campaign only gives a mech a chance of not being slagged on 7+ if destroyed during the mission.
battle size is important - how long do you want the game to be? i'm not as familiar with the pacing of AS games, but I always try to keep my campaign missions finisable in three hours with a way to have clear objective resolution if time runs out.
planning is important - i start with the big picture: setting, background, and major objectives (e.g. find who in the AFFS is selling arms to capellan-backed rebels in the chaos march or capture a key spaceport to support the main allied landings on Cor Caroli). then make sure you create a reasonable framework to get to that objective. I usually do three phases of 4-6 missions... but for a book, maybe three phases of three or two of four to keep yourself sane.
missions should have clear consequences for objectives completely / not completed. didn't destroy the spy's rotunda? he got back to report your position and now an enemy armor company shows up turn five of the next game. Successfully destroy the ammo depot? Enemy units can't use their LRM, SRM, AC, etc abilities (or spotrule a -25% damage to non-ENE mechs for the remainder of the campaign phase). branching missions can get messy but the above is doable with an IF/THEN paragraph in the next scenario.
if you plan on releasing it for others to play without you, playtest the scenarios.
i'll add more if i think of anything
