-Plastic clips that hold the headliner to roof (3 in the rear, 2 in the middle and 2 where the driver's grab handle should be, i believe) are prone to breaking if you dont pull them PERFECTLY even.
-Dont break the front seatbelt adjusters when removing the belts. That's another common newbie mistake.
-I usually like to remove EVERYTHING that holds the headliner except the sunroof rectangular trim discussed earlier and the trim piece at the top of the hatch opening. Then get someone to seat in the front seat while you sit in cargo area, and support the headliner while removing both trim pieces. It's not VERY brittle, but will break if you're not careful. It usually breaks on the sides of the sunroof opening, so it's best to hold it just in front of the opening.