I'm in the same boat right now, And I'm f**king loving it
Just keep your cool, Keep her at arm's length and don't go diving in head first, take it slow and make sure that you're prepared whatever the outcome.
Try not to get too attached and let her do the chasing for a bit, she's come back to you after all.
Just because you've been together in the past doesn't mean it's gonna go bad a second time, just start over from the beginning and see where it goes, try not to dwell on the past and focus on the present