Once the scaffolding is up, start by trimming out all the windows and painting the trim. It seems a little backwards, but you'll get a much crisper line between the trim and shingles if you butt the shingles to the already painted trim. We ordered the color-matched caulk from James Hardie and use a small bead to fill the gap. The caulk has a different sheen than the shingles, which telegraphs even from a distance, so keep the use to a minimum.
One thing to watch out for is waterfalls in your alignment. Fortuantely, this one on the back of the house was caught early enough to stagger the spread above the doors. See the vertical line of wide shingles?
At interior corners, we ran a piece of vertical wood trim for the shingles to butt into, and at exterior corners, we used these 199 Series metal corner trims from Simplicity Tool Corporation which conveniently come in all the standard James Hardie Colors. I was nervous about the metal corners standing out because of the difference in texture (I ordered the smooth version), but they really go unnoticed.
The panels install quickly over the large expanses, but that time is easily lost when you bump into a window and have to make several cuts per panel to get them to perfectly align. Overall, I think these things are awesome! It's so satisfying to have the house look this finished after siding without the long wait for paint.