How should i talk to this girl?

Well this girl said happy birthday to me on my wall on fb and i havent talked to her in a while. we used to talk all the time a couple years ago so i messaged her satin hi and if she remembered me and she say yea so it went from there and then i say we should hang out somtime and she say she down so i gave her my # and said txt me then she said no i should text her and gave me her #. so how long should i w8 to txt her bak cuz shes seem cool as hell and shes hot so wut do i say to her wen i txt her