1. Do NOT pay before you take delivery. Try to find the car in the lot and give it a pre-delivery inspection, especially the paint, in good lighting conditions. Don't let them scare you away. I went with friends a couple of weeks ago and while they were in the store, I found the car in the lot and found paint defects and assembly issues, they rejected the car and did not pay for it, they now have a new car ready for pick up next week, and this time the delivery center knows not to screw up.
2. Do NOT be afraid to highlight defects and point them out and do not accept the "its within spec".
3. Bring a third party to inspect the car while you are taking care of business or simply waiting, its very hard to concentrate when you are excited about delivery and are being rushed to fill out documents.