Video by my ever-awesome collaborator, noahw.
Step 1: Obtain Squid
If you purchase squid, make sure they are still whole- if they're pre-cleaned all of that wonderful ink will be gone!
A fresh squid has reddish-brown spots on a white or cream-colored body- if the flesh has started to turn pink or smell, buy your squid elsewhere. Boxes of frozen squid should be solid, without evidence of leakage or freeze-thawing. Small squid are tastier and easier to cook, but they have less ink.
Step 2: Remove ink sac
First, pull the head and tentacles out of the body cavity. The guts will come along with the head: look for the small thin silvery sac about halfway along.
Carefully detach the ink sac, taking care not to puncture it. It's attached at the ends, so just slip your knife underneath and cut away from the center to remove it.
Step 3: Prep container
If you're going to print with your ink, put a tablespoon of matte medium, linseed oil or other ink carrier medium into the bowl. To cook with your ink, use a tablespoon of water or vinegar instead. It's easy to dilute your ink later- start concentrated now to keep your options open.