Get some space from your ex. Although it might not seem possible, do your best to put him out of your mind. Avoid going to places where you typically went with him or doing things which you often did together. Avoid contact with him for now, even if you'd later like to remain friends; this period is important for coming to terms with the breakup and learning to get by without your ex in your life.
Schedule more activities with your friends. Your friends can give you fantastic support, and you shouldn't feel guilty about accepting it. Let them take you out, and keep an honest line of communication with them. If you're used to confiding all your emotions in your ex, it may take awhile before you feel comfortable speaking about your feelings to your friends. However, doing this can be healthy and can assist you in developing a sense of perspective.
Change your environment. Redecorate your room, schedule a vacation and maybe even change your wardrobe a little -- all of this can help reinforce the notion that you're entering a new chapter of your life, and it can inspire you to feel more confident at the same time. Making changes in your life can also keep you focused on the future, preventing your mind from persistently thinking about your ex.
Be positive. Surround yourself with comforts and things that you enjoy; read a book from your childhood, visit your favorite amusement park or watch your favorite films. Doing these things will remind you of happier times and will inspire you to remember what life was like before you met your ex.