How do I get my best friend back?

Well, I recently lost my best friend of four years. (About 8 months ago). I've tried talking to her and we've gotten closer than we were, but we still aren't as close as we used to be, and I really want to regain our amazing friendship. I miss talking to her so much and when we do talk I get so happy and so regretful. We start high school this coming August and I want to know how we can revamp our friendship! Thanks!