my advise same as most of the ppl here, dun do any revenge, maybe just let she feel regret then is enough..
u must think that is her lost that she leave u, is her wrong decision that she wan that guy not u..
how to make she regret?carry on ur life as usual, if got chance to know new gf, then make ur new relationship better than ur last relationship(with ur this gf)..perhaps she know u have a good relation wit other gal and happier than the time u wit she, she definitely will jealous and regret why she dump u last time..
at last, this is all my opinion only..thx