Give yourself the necessary time to heal. You won't immediately feel better overnight. Chances are, you'll slowly feel better and better until you're no longer grieving over your failed relationship. Until then, though, be patient with your emotions and feelings. As long as you're not dwelling on every aspect of the breakup, there's nothing wrong with taking baby steps to feeling like yourself again.
Avoid your ex and her family, social circle and spots where she may visit, at least for the time being. You don't have to run in the other direction if you see her coming, but avoiding the triggers that will remind you of her and bring up sad feelings is necessary right after a breakup. Even minor contact between you two will make it difficult to move past the relationship.
Talk to people in your social circle or family whom you trust. Finding one or more reliable friends can help you to talk out your feelings and cope with the breakup. You may even want to join a support group for people in a similar situation. Going through a breakup alone can cause extra, unneeded stress.
Maintain your physical health. Even if you emotionally and mentally feel like a wreck right now, it's important to keep your body healthy, even if it's difficult. Turning to alcohol, unhealthy foods and drugs will not help you to cope; instead, you'll feel less healthy and worse overall. Get as much sleep as you can, don't overdo it on the coffee, exercise lightly and eat nutritious foods. Remember, relaxation is part of health, too. Make sure to take time for yourself, to breathe deeply and clear your mind.