Saying "No" Is Difficult

I'm a people pleaser.  My parents often reminded me that i needed to be careful about what other might think of my actions.  When I went with my Fist Baptist Church of Norman, Oklahoma, youth group to our summer camp at Falls Creek we stayed in the church's dorm.  On the steps of the dorm, someone had used marbles in concrete to write the word "Others."  So, I got this people pleasing identity from both my parents and my church.  This makes it difficult for me to say "No" to people, invitations, situations, etc.  When I do say "No", I want them to understand the reasons for my answer so I over-explain.  My over-explaining is an attempt to defend my "No" and it rarely works for either me or them.  I had a friend who said that one needs to be like a surgeon when saying "No."  By clean, quick and specific.  No one wants to be under a surgeon's knife who seems unsure, unsteady with the knife and makes cuts that are too much.  I'm still working on this skill of saying "No."  I tell others that every time they say "Yes" to one thing they have said "No" to many other possibilities.  I need to listen to myself more often, but that means I need to say "No" to listening to all those other voices in my head.  Saying "No" is difficult.