Wash - usually. Starch - generally not.
I have a "Why you should prewas fabrics" story. I made curtains for my sewing room - just basic rectangles and I lined them with muslin. All the fabric came from my stash. I was so proud of myself that the pattern lined up and everything, and then I washed them...... Well, the lining shrank at a different rate than the main fabric and suddenly my curtain looked like it wore a slip that was too long.