1. Remove the temptation of easy access. Delete his or her number from your phone, block 'em on Facebook, get rid of old emails. Unless you work together or share children, there is really no need to initiate further contact. (If there was no major betrayal before the breakup, you may wish to maintain the friendship; in this case, just lay low for awhile and get some emotional distance.)
2. Do not keep tabs on your ex. This means no Facebook stalking (covertly or otherwise), no asking around, no driving past his or her house. If it's over, it's over. Let them wonder what you're doing or whom you're with now, but resist the temptation to keep that wound fresh.
3. Let it out. Write all your feelings in a notebook, a personal blog or journal, anywhere that you can vent and detox those negative feelings.
4. Decide that, since you have now detoxed, to turn over a new leaf. Think of this as a positive opportunity to make a fresh start, and adopt a positive attitude.
5. Take care of yourself. Eat healthy, exercise, and generally treat yourself well. This is especially true if you were with someone who was not terribly concerned with your physical or emotional well-being. When you take responsibility of your own well-being, you're taking control of your life.
6. When you're feeling down on yourself, try thinking of all your positive qualities. Make a list if you have to, in order to refer to it for future falterings.
7. While you're in the habit of making lists, try making another one of all the reasons you're better off NOT in the relationship that you used to be. If your former partner was annoying, unsupportive, selfish, or boring... write it down. Absorb it, realize that the end of the relationship is a positive thing, and move on.
8. Socialize with friends. Call people that you haven't spoken to in a long while. Re-establish touch with long lost friends, and enjoy reconnecting with those who love you.
9. Pursue new interests, or revive much-beloved older ones.
10. Take the focus off of yourself. Realize that other people have issues too; do something wonderful for another person, and enjoy the glow that comes along with it.
11. Pleasure yourself physically. 'Nuff said.
12. Make changes to your apprearance. Yes, it can be a bit of a cliche, but the truth is that seeing a cool new you in the mirror can help to alter your own perception of yourself. Change your hair, try a new fashion style, get your most trusted cohorts together and devise an interesting new look for yourself.
13. Change your surroundings. You may not be in the position to move, but sometimes when you feel down in the dumps, and everything reminds you of your ex, you want to switch things around. Move the furniture, paint the walls. Burn some sage and detoxify your space. If you're not interested in switching around your space, even a good thorough cleaning can make you feel fantastic.
14. Throw yourself into your work for awhile. Don't become a workaholic, though!
15. When you're ready to see new people, try dating. Keep in mind that "rebounds" usually don't work out, so don't go hunting for a new relationship right away. Just enjoy socializing, flirting, and meeting new and interesting (or not-so-interesting!) people.
16. Make new friends.
17. Find enjoyment in solitary activities like reading, video games, or just walking through your city and seeing the sights.
18. If your ex dumped you for someone else or was a particularly big jerk, think about the next person they end up with. Instead of feeling jealous or tearing them down, realize how being with the ex totally sucks. Feel simultaneously sorry for the "latest victim," and relieved that your ex is no longer your problem.
19. Truly evolved people never stop growing, changing, and learning. Try filling your mind with new information and perceptions. Expanding your mind will expand every part of your life.
20. Love yourself and love others.