First, allow yourself time to heal from a bad breakup.
You don't have to downsize your sadness for anyone; it is really hard to let go of a person that you thought you loved. Let yourself feel however you need to, get it out of your system, and you will be ready to move past those feelings faster.
Once those initial sad feelings are under control, push yourself to go out and spend time with friends and family or whoever company you enjoy.
After a breakup, don't contact that person.
Even if you are wanting to maintain a friendship with that person, waiting at least 6 months before you start to talk again can cut out any of the confusion or heartache that comes from both people after a relationship has ended. Also feel free to toss out any old mementos of the ended relationship; why hold onto it?
After a bad breakup, keep yourself busy.
Pick up a new sport or hobby. Use all of that extra time you now have to gain a new skill.
Whatever you do, don't idealize the past relationship.
When people break up they often remember the relationship as being much better than it actually was. Remember why you broke up, and this of these more sour parts of the relationship whenever you start to miss it.
If you have gone through a bad breakup, try to think of this as an opportunity.
If the person was silly enough to let you go, they obviously weren't deserving in the first place. Now, you have your freedom back, your independence back, and the opportunity to potentially meet someone who is a better match for you.
Don't jump right back into a relationship after a breakup.
There is absolutely nothing wrong with being single; embrace it. After a breakup, try to spend some time alone before you commit to another person again.
Success is the best revenge.
Take care of yourself, further your education, snag that job you really wanted; whatever your vision of success, go after it.