You'll appreciate your life when the majority of your thoughts remain positive. Negative thoughts can sometimes be overwhelming, and just because you have them doesn't mean you're a bad person. They happen to everyone, but you can strive to keep them to a minimum with the help of a grateful attitude.
One way to show your gratitude every day is to remind yourself of the big picture when a negative thought arises. If a petty argument with a friend makes you feel angry and heated, take a deep breath and think for a moment. Remember that the argument is not permanent and, instead, feel grateful for the gift of this relationship.