When you bump into your ex, you want to give him/her the impression that you're happy but busy, even if that's not strictly true. If your ex sees you moping around in the mall, sad and depressed, they're definitely not going to believe that you've moved on.
When you see your ex, smile a few times at him or her, but not in a flirty or longing way. You want them to think that you're happy because your life is good, not because you saw them. Try not to let any of the unhappiness you experienced during and after the breakup ruin your mood.
If your ex asks you about how you're doing, focus on only the good, not the bad. That competition you won last weekend? Tell them. That school you got accepted into? That too. Don't lie, but focus on your accomplishments rather than failures.
Don't make time for him/her. This will make them think twice. Say something like, "Oh, I'm just about to meet a friend, good talking to you," and walk off without looking back. Do this relatively early on.
2. Take time to respond to his/her messages, texts, or phone calls
Nothing says "I'm desperate" than when you immediately answer your ex's texts or phone calls. Take your time. Take a couple days to respond, pretending that it's really not a big deal.
3. Publicize all your fun new activities and interesting friends on social media.
The internet is a great way to convince your ex that you've moved on. Facebook, MySpace, and Twitter are all golden opportunities to publicize your newfound freedom.
Take plenty of pictures when you're out with your friends, especially when you're having a blast. Going out to the beach? Take a picture and post a caption with something like "Tamed two beaches in two days with my two best friends. Beach bod, say hello to summer!"
Stay a little mysterious. Have your ex and their friends wondering what you're actually up to. Post something a little mysterious to your social network that will get your ex thinking about all the cool things that you're doing without him/her.
4. Don't show any signs you care
It's perfectly okay to still have feelings for your ex, but if you want to show them you've moved on, they can't know about those
Don't Go to his/her parties or special events. Make up an excuse if you have to.
Don't Pay him/her compliments.
Don't Call your ex "just to talk." If you need to talk, have something specific in mind you want to talk about.
Don't Get caught staring or looking too long at your ex. Try pretending they're not there.
5. Be seen with other dates
The best way to show your ex that you've moved on, of course, is to show him/her your other dates. Not only will s/he know you've on, they'll probably be at least a little jealous, too. Double whammy!
Be seen, but be classy. Letting other people — including your ex — know that you're seeing other people doesn't mean you have to be in their face about it. Be seen going to the movies, going to dances, and flirting, but don't be seen doing anything you'd be embarrassed doing around your parents (i.e. kissing, making out, etc.).
If you really want to get a little revenge, try dating one of your ex's friends. Be warned, however: this could hurt their friendship and your ability to get back together with your ex.
6. Act like you've been there before
Act like you know the program. The signs you show your ex directly are one thing; but the signs you show the rest of the world reinforce what you show your ex, and they help you actually move on, if that's what you want to do.
If someone asks you how you're holding up, say something like: "You know, any breakup is hard. There were parts about [your ex] that were great. But after we broke up, I realized the parts about [your ex] that weren't so great, and now I'm focusing on finding someone who can change that."
7. Go traveling or take a trip if you can
Nothing says "I'm not going to let this breakup keep me down" quite like a good trip will. Some people travel to far-flung places like India or Tahiti after a breakup, but all you really need to do is find a change of scenery, even if that scenery is only an hour away!
When you're out and about, hang out with the locals. There's no better way to forget your sorrows than learning from and partying with the locals.
Remember to publicize your travels on social media! Never pass up the opportunity to brag about where you're going to the rest of the world, especially if it's a darn cool place.
Try different things. Be adventurous. Be curious. Put yourself out there. Very few people regret doing this once they've summoned up the courage to try it. It'll help soothe your soul.
8. Don't get caught talking or dreaming about your ex
If you're constantly talking about your ex to your friends, chances are they'll eventually let it slip, and that information might get back to your ex. Then s/he'll know you haven't moved on. It's best to confide only in your absolute best friend what's going on, and forget about your ex the rest of the time
9. Pick up a new hobby, sport, or pastime
To help keep you preoccupied, and to help keep your mind from wandering, consider taking up a new hobby or really getting back into an old one you gave up.
Sports have the added benefit of giving you a great workout while you have fun. Going to the gym and hitting the treadmill every day can get boring, but playing 3 on 3 half-court is about as fun as it gets.
Try something that will push your limits. Breakups are opportunities to get to know yourself better. Why not learn about yourself by trying something you never would have thought you liked? Glass-blowing, rock climbing, wildlife conservation — whatever it is, keep it fresh!
10. Find the real you.
In order to move on, you need time to yourself to think like,"Who am I? Is this really me?" Spending time on yourself will allow you to truly move on and feel detached from your ex. The more confident you feel, the easier dealing with confrontations or meetings with your ex will become.