As I've stated before in various posts, I think people break up for a reason. Unless BOTH parties involved are seriously committed to making the return a success, things are definitely doomed to fail again. But I think that holds true for whole other relationships as well.
The thing to consider most is why you want to be in a relationship at all, let alone with this person with whom you split in the first place. Is it loneliness? Because if that's the motivation, DO NOT get re-involved. Is it love for each other, but with some other conflict; something unresolved that would creep up again? That needs serious work from both you and your ex, as I said already.
Know thyself. Understand where you're coming from, and where your ex is coming from, and what the heck you want out of a relationship. Perhaps you just want to casually date. <shrug> I can't suggest what I don't know from that standpoint. But I do know that relationships are darn hard work, and although I have my own slew of failed ones, I hold firmly to the belief that mutual hard work is extremely well worth it.