Some common mistakes people make when trying to restore shrunken garments include using hot water or harsh detergents which can further shrink the fabric or damage its fibers. Another mistake is wringing out the garment forcefully instead of gently squeezing it, leading to misshaping and potential tearing. Not allowing the clothing to soak long enough in the lukewarm water can also result in ineffective restoration. Lastly, not carefully stretching the garment while it's still damp may cause uneven stretching or distortion of its shape.