Step one: Find a cool, dark cupboard. Not above the stove (too hot), not by the window (too sunny). A quiet little spot. Like a hobbit hole for condiments.
Step two: Keep the cap clean. Wipe it after use. Mustard residue can crust up and make the lid sticky. You’re not a slob.
Step three: Embrace the shelf life. Yes, it might eventually darken or separate. That’s fine. Give it a shake, and it’s back to its zesty self. Mustard is resilient.