The most successful way to say “No”
"Negotiated 'No's'" work by making other people think about the consequences of what they are asking you to do. They work pretty well and they are fairly easy to implement BUT their power comes from the other person's willingness to back down. In effect, they are a short-code for you saying "Please don't ask me to give you my time."
However, the real power is released when you start to assert your unwillingness to give away your time rather than depending on their willingness to let you keep it.
This version of "No" is expressed as "No! Because..."
Put simply, you are saying a straight "No" and then explaining why you are saying that. So, for instance, if someone in your organisation emails you and asks you to put together some information together for them that day and you know that it will take several hours (that you don't have) then you could say something like "Sorry, I can't help you this time because my day is already jammed full." This is not a negotiation. It is a refusal with an explanation. It is a high stakes version of "No" and it will not always be appropriate but it is very effective for pushing back when people are starting to "abuse" your goodwill or trample on your boundaries.
What makes this version of "No" so effective is that its power comes from you NOT the other person. You are basically saying to them:
"No, you can't have my time and here's the reason why."
The key to using this version of "No" successfully lies in the second half of the statement; the reason why. This is not just a message to the other person that you have good reasons for saying "No", it's also a message to yourself that you HAVE to say "No".
It's a reminder to you of what you will lose/miss out on/fail to accomplish if you say yes to the other person's request. It is thinking about these consequences that will boost your determination to protect your time for the things that really matter to you.
Focussing so much on saying "no" may seem a little negative and you may feel that it would make you a bad person to be so determined to say "No" but that is not the case. We don't say "No" to be mean to people, we do it to make time for the things we are really supposed to be doing.