Find a way to spend most of your time doing things you are passionate about. This can be a hobby, faith, friendship or spouse.
Try to avoid staying in relationships, jobs, or lifestyles in which you are comfortable, but not wholly satisfied.
In short, gratitude is no substitute for passion.
For example, you may be grateful that you have a well-paying job, but if you are not passionate about your career, most of your time will be spent longing for something more worthwhile.
Which brings me to my answer: The meaning of life is to strive for things you can be passionate about. If you're lucky, you stumble upon a few of them early in your life.