Okay who am I kidding? "The nice way"? There IS no nice way to break up with her, especially if you two have been in a long term relationship.

However, all hope is not lost. You can still drop the anchor on her gently. You know, so that you won't be given nasty looks by her girl friends and walk around as if you've got "Insensitive Jerk" plastered across your forehead. And here's how.

Break-up Tip #1: Know what to say
After she realises that you're about to break up with her, no words that come after that will make her feel better. But it's even worse when you're stuttering and suddenly you find that you haven't said what you wanted to say before she stalks off, probably to bitch about you to her friends. It is always better to collect your thoughts, commit them to memory, and rehearse. That way you minimise the chances of awkward silences and the need for improvisation, which has a nasty habit of steering you into territory that will crush her.

Break-up Tip #2: Choose the right setting
The last thing you want to do is tie her favourite place to a horrible memory of a bad break up. So choose a neutral setting and be sure to see that she's not tied down by anything important. Make sure she's got enough in-between times so that she'll be able to pull herself up before her next meeting.

Break-up Tip #3: Be honest
When it comes to breaking up, being honest will be your salvation. But of course, this isn't permission to inform her of her every shortcoming. Or be harsh to her in any way, getting dumped stings enough as it is and there's no reason to add salt to the wound.

Break-up Tip #4: Avoid blame
When a relationship turns sour, it shouldn't be any one party's fault. Your best bet is to shy away from pointing fingers and direct attention at the central issue: Incompatibility.

Break-up Tip #5: Be empathetic
When you're choosing your words to say, put yourself in her shoes so that it will ease picking words that will cushion the blow.

Break-up Tip #6: Don't get into a fight
Note that this conversation could push her to the end of her fuse, because face it, she doesn't want this and she's not going to agree with you whole-heartedly. If she loses her temper, it's very important that you keep yours although it may be difficult. There's no point in talking things out if both of you are getting all emotional and worked up.

Break-up Tip #7: Be prepared to cut off your speech
There's always gonna be a possibility that she'll walk away before you've said everything you wanted to say. If this happens, don't chat her out the door. Understand that she's trying to salvage the pieces of a shattered ego and doesn't want to be seen in a compromised condition. She'll follow up if she needs closure.

Break-up Tip #8: Keep your distance
From the moment you go your separate ways, give her plenty o physical space. And this means no bumping into her at your usual rendezvous spots. Give her time to adjust to your absence and potentially flush everything ou ever gave her down the toilet.

Break-up Tip #9: Don't discuss your new relationship
"We can still be friends" is, surprisingly NOT what she wants to hear. That will mean putting emphasis that you are not together. Should you remain friends after the break up, then good on you. But don't make it seem as if you're making sure that you're nothing more.

Source: Breaking Up [AskMen.com]