Learn to be Assertive and Love it!

Credit: Getty Images

With friends and family

Surprisingly, your nearest and dearest can be the toughest to stand up to. "They're the people we want to please the most," says Miller. "We'd rather be unhappy ourselves than disappoint them." To complicate matters, we have to fight a lifetime of old (bad) habits—saying "sure" when we really mean "no way."

True, standing your ground can be momentarily uncomfortable, but it's so worth it—your relationships will be stronger as a result, Miller says. Try these tactics:

Next: Saying "no!"