The standard impossible-to-answer philosophical question, which has become very much a cliché, is “What is the meaning of life?” I've answered this for myself ages ago: life has no meaning by itself. Everybody can create as much or as little meaning for his or her own life as they please.
It helps to have an ultimate goal in life. For every decision you need to make, you can check whether it aligns with your life goal. Having a goal also gives your life purpose and motivate you to keep going.
When I read a post by Steve Pavlina a couple of months back, I was reminded of this. What was my goal in life? Steve suggests to write down potential goals until one makes you cry — that is the goal you're looking for. I discovered I didn't need this: the answer popped right into my head, and had probably been there for a long time.
All that remains is to write it down. My goal in life is to continuously keep improving myself, and thereby the world around me.
I'm a pretty altruistic person. Yes, I want to improve the world. But I also have a selfish part. I want to grow, to learn, to become a better person in every sense. These goals don't have to be in conflict. A “good” me also cares about his surroundings, helps other people, tries to make a difference for the better. That's the person I want to be.