TRAIN your mind to see the good in every situation. It won't come naturally, you WILL have to work at it, but eventually it will become second nature and you will have joy in your life even when things aren't going your way.
Replace negative thoughts with positive ones. As soon as a negative thought enters your mind, acknowledge it, let it go, and select a positive thought to replace it. Practicing this line of thinking will improve your life, for the better.