From this article by John Piper:
1. The excellence of the products or services you render in your job shows the excellence and greatness of God.
2. The standards of integrity you follow at your job show the integrity and holiness of God.
3. The love you show to people in your job shows the love of God.
4. The stewardship of the money you make from your job shows the value of God compared to other things.
5. The verbal testimony you give to the reality of Christ shows the doorway to all these things in your life and their possibility in the lives of others.