How do I say sorry to best friend?

I've known my Best Friend since kinder garden and I have a very bad habit of swearing, which she does not like. I think my habit had gotten so bad that she got really tired of it and just stopped talking to me. We haven't talked in almost three weeks now. We used to talk every single day for hours on end. She told me on twitter that I've been acting weird lately a few weeks ago. How do I tell her I'll try to break my habit so we could be friends again?