Bundles in the attic. I recommend stretching them in the opposite direction you are installing and laying them flat. One of the most tedious things about the project is trying to pull individual strands from the bundle to install while keeping the rest of the strands from tangling.
a much easier alternative is to use glow-in-the-dark stars you affix to the ceiling with poster glue. or just straight glow-in-the-dark paint. you'll get the star effect for awhile, then they'll gently fade as you fall asleep.