I have to say that there is no easy way man, you have to either tell her straight up, or just don't do it. Make sure that you tell her why, because she would be miserable wondering "why", and what she did wrong. Try not to be friends immediately, it will be really uncomfortable for both of you. Hang out with your friends a bit more, get used to being single again and it wouldn't hurt as bad on your side, or make you go running back to her from out of misery. I just got out of a year and 5 months relationship. These are the things that i did, and it worked out great for me, we both moved on with no problem.
Good luck man.
-Greg
