Been dumped yourself? The quicker it is, the more painful it is, the easier and quicker it is to deal with.
My last ex explained that she wanted to cool things off, we'd still "be b/f and g/f but with less commitment". What she meant was "you're dumped" but it took five weeks of no sex, argue and general headf*** before she'd admit that's what she'd meant all along... and she had a new boyfriend. She just couldn't handle confrontation. Cow.
The last time I got dumped before that it was just "I don't think we should go out any more"... I was gutted but over it in a week.
I've really had it up to here with my girl, she' making my head hurt like a botched trepanning session...
I figure she's told me enough times she wants to be with me for life, and if I felt that about someone I'd want them to give me a good last chance... but the ice is thin and she's skating with a backpack full of lead.
One final thing, be compassionate: DON'T dump her the morning before her job interview/ the morning her mother died... unless she's really pissed you off in which case do it and do it for all us guys

Best is the day before she's due to spend time with female relatives or friends, esp if they're going on holiday (added bonus is she'll be out of the country and out of harms way). They'll spend a few days calling you things you'd never want to hear, slandering you, being vicious and plotting revenge, but at least she'll feel better about it all and recover quicker. If necessary, call her sister and ask when would be a good time... Sister will probably arrange to go and look after her.
Breathe, it's done, it's over.
Then screw the sister.