Be sure where you stand first, i.e., whether you want to say yes or no. If you're not sure, say you need time to think it over and let the person know when you will have an answer.
Ask for clarification if you don't fully understand what is requested of you.
Be as brief as possible, i.e., give a legitimate reason for your refusal, but avoid long elaborate explanations and justifications. Such excuses may be used by the other person to argue you out of your "no."
Actually use the word "no" when declining. "No" has more power and is less ambiguous than, "Well, I just don't think so..."
Make sure your nonverbal gestures mirror your verbal messages. Shake your head when saying "no." Often people unknowingly nod their heads and smile when they are attempting to decline or refuse.
Use the words "I won't" or "I've decided not to" rather than "I can't" or "I shouldn't". This emphasizes that you have made a choice.
You may have to decline several times before the person "hears" you. It is not necessary to come up with a new explanation each time, just repeat your "no" and your original reason for declining.
If the person persists even after you have repeated your "no" several times, use silence (easier on the phone), or change the topic of conversation. You have the right to end the conversation.
You may want to acknowledge any feelings another has about your refusal, "I know this will be a disappointment to you, but I won't be able to..." However, you don't need to say "I'm sorry" in most situations to apologize for your refusal. Saying "I'm sorry" tends to compromise your basic right to say "no."
Avoid feeling guilty. It is not up to you to solve others' problems or make them happy.
If you do not want to agree to the person's original request, but still desire to help her or him out, offer a compromise: "I will not be able to babysit the whole afternoon, but I can sit for two hours."
You can change your mind and say "no" to a request you originally said "yes" to. All of the above applies to your change of mind. University Counseling Service, The University of Iowa, 3223 Westlawn S, 52242-1100, 319-335-7294