I recently had to say no to a project. It was something I enjoyed, but as I meditated on my energy levels and what I needed to accomplish in the next month, I realized I was just taking on too much. I knew that saying no would disappoint some people, but I needed to be firm.
I was reminded of Byron Katie, and how she always says no with a smile.
Sometimes it is hard to say no to people, especially when they are people you like and respect. If you sit back for a moment, you may realize that there are certain people in your life who just command involvement. This does not mean they are controlling or bad. It just means they are firm in their vision and what they are doing. They will ask you to participate with such charm and confidence that you may find yourself saying yes without thinking.