This is from personal experience. I've been down that road.
Despite hearing that this is a bad idea, you're going to go through with this. I know because I've done it more than once.
Anyway... enough lecturing (said in a friendly tone).
Here's what you do...
You look your absolute best.... but you do not give any sign that you are interested in her. Nothing! You're probably thinking that this goes against everything you've been conditioned to think. Nevertheless, you don't want to appear like you're on trial and hoping for parole. You want to give off the image that you are your own person and she holds no keys.
Don't be confrontational or put on some show or anything.
Instead, you want to come across as confident, independent and fun! What ever you do, don't get into deep conversations. Instead, if something comes up about the relationship history... just say ... "I'd rather not get bogged down with the past."
Keep it fun and keep it very short! You don't text, e-mail or call her afterwards...
You let her mind wonder. If you do the above, it will.
She will eventually reach out (assuming you pull off the above).
When she does, post here about details. You'll get a lot of flack from some forum members, but some others will provide you some tips.
Again, I don't advocate revisiting an ex from the past, but you're going to do it anyway and I know this.
Good luck.