9. "You should join a gym."

Variations: "You should walk more." "You'll never lose weight by exercise alone."

Why it's unhelpful: "You should" comments come across like criticism, even when you mean them constructively, and even though it's true that the key to losing weight is to manage exercise as well as diet.

Better: To help the person who's losing weight get more exercise, make a string-free offer that sounds like help, not an attack: "Do you want to join the Y with me?" "I'm walking the dog; do you want to come?"