Keep your time occupied. Do stuffs that you have never done before. Explore. Socialize. Expand you life. It's okay if you think of her/him sometimes. Avoiding to think of him/her will only make you crave or think of him/her more. Have a list of goals to accomplish and focus on these. Exercising , too, can help. Cry if you want to. It's okay. Don't be bitter, be better.