In a word: LOTS! AND LOTS! (OK three words!!)
Being grateful produces so many physical, social and psychological advantages that I am amazed it isn’t taught in schools! For example, it opens you to positive emotions and gives them space to breath and grow;  it makes you more respectful, more joyous; it helps you cope better with problems; and it strengthens your relationships to your self and others. Why wouldn’t you want to be more grateful?
Do you wish to be happier? To forgive more easily? To be less stressed? To see more clearly what the point of your life is? To be less fearful. Less tense? You can – with gratitude. Why wouldn’t you not want to be more grateful?
If you’re not being grateful then there is a strong tendency to see and feel what is missing from your life. Not a nice feeling. And … if you go down that road, you’ll end up in the land of pessimism. So, there you have it – be more grateful.
All this is waiting for you. But … you have to do it, of course.