Well, most of us can make a great day by faking it and telling to ourselves that today is a great day. :D Why must fake when you can actually feel great! Well the simple and most common ingredient is smile! Simple right? Think positive and smile all the way down.
Think about your love ones, your friends or even your pets. Those subjects can make you smile instantly. Think about the positive things ONLY. Do not torture your mind and soul by always thinking about the negative ones. If your friends hate you, never mind. They are just useless. Hehe. Well, say good things about your own self. Find things that you can relate to happiness. :) And you will be having a great day. Keep laughing and watch comedies. Go to the gym. Enhance your adrenaline. So sweat! Do everything that you can do to maintain your happiness.
Be happy and stay positive! :D