In my experience, I started by saying yes to everything and getting burned. Then as I got older, I learned to say "no" and how say/how not to say/how to imply "

In my experience, I started by saying yes to everything and getting burned. Then as I got older, I learned to say "no" and how say/how not to say/how to imply "no". At first it's hard, but people will learn to accept your "no"s and is a sign of respect when they stop questioning why you said "no". (assumption: no is backed up by reasonable and rational reasons)