First try to put a rag in the mast below the lower shackle, in hopes that it will catch anything you drop.
I find it's easiest to get the tack into the lower slot before starting to put the head into the upper part. For the head, I've had good luck putting the shackle onto the webbing first, then sliding it through the slot and installing the bolt. I found that was easier than trying to put the shackle into the webbing after it was already inside the mast. Have the furling line a little slack so that you can turn the foil to line up the shackles with whatever opening you want to work through. The hoist itself should be pretty easy once you have everything attached - just help guide the sail into position to enter the track.
Oh, and have an extra set of Allen wrenches, just in case one finds its way to the bottom of the mast step.
The good thing is, once it's done you don't have to think about it for about 6 months.