This has been a big battle for me as well. After years of suffering through some pretty bad bouts of them (I think the worst was when I kept getting them on the top and bottom at the same time, so they'd fuse together at night
), I finally got a prescription ointment. I don't have it on me and can't remember what it's called though. I'm in Canada, and it wasn't by the same name as the ones I see in the US.
Anyway, I've only had two outbreaks since then, and they're less severe. After trying every remedy I could find online, I think the only one that really, really worked for me (and still does, in conjunction with the ointment) is ice. If you can get it AS SOON AS YOU FEEL THE TINGLE and numb the shit out of it with ice as much as you can stand, it prevents the rapid multiplication of the cells. Even before I got the prescription, I could sometimes ward them off like this.
Aside from general life stuff that can provoke them (stress, hormones, etc), keep your lips in good shape with a good lip balm regularly.