This is especially hard when you are a people pleaser, so often times you end up committing to things you don't want to do, or if you are able to muster up the nerve to say no, you find your self rambling on with an excuse about why you are unable to accommodate them.
I struggle with this, but I have made improvement. I am learning that just because someone asks you to do something does not obligate you to do it. And it does not obligate you to give an extended explanation of why.
This is something that does that not come naturally for many of us. It is something that requires work. It all ties in with being independent rather than codependent. You are responsible for your own decisions and your own happiness, not the decisions and happiness of others.