How can I become good friends with my ex again?

So I was good friends with a girl we would talk all the time and she liked me I asked her out. It was my first relationship then I broke up cause I felt like a bad boyfriend. We were still friends didn't talk as much as before. After a few months I realized I really did like her a lot and I asked her out again. She said no, but was sorry for me we started talking even less...I tried getting her back but didn't succed she moved on. So after a while I decided to also. How do I get her back as a good friend again? I miss talking to her I know I'm probably not gonna get her back but she means a lot to me. How do I build a better friendship with her?