To make the best use of your life, you must never forget two truths: First, compared with eternity, life is extremely brief. Second, earth is only a temporary residence. You won't be here long, so don't get too attached. Repeatedly the Bible compares life on earth to temporarily living in a foreign country. You're just passing through, just visiting earth. We are preparing for something even better.
Realizing that life on earth is just a temporary assignment should radically alter your values. Eternal values, not temporal values, should become the deciding factors for your decisions.
When life gets though, when you're overwhelmed with doubt, or when you wonder if living for Christ is worth the effort, remember that you are not home yet. At death you won't leave home. You'll go home.