"And the LORD was with Joseph, and he was a prosperous man; and he was in the house of his master the Egyptian. And his master saw that the LORD was with him, and that the LORD made all that he did to prosper in his hand. And Joseph found grace in his sight, and served him: and he made him overseer over his house, and all that he had put into his hand...and Joseph was a goodly person, well favoured." (Gen. 39:1-6)
Joseph's influence could have been stopped the moment his brothers threw him down the pit and then later sold him to slavery. He had what seems to be every 'right' to become bitter. This is not a matter of positive thinking or false piety. Joseph knew that he could trust the LORD in hard cases and evidently he did. Despite these strikes against him, God is still in control. God had a plan, and all the people in this story is used by God to accomplish His will. We also don't see Joseph taking credit for any of his success. Potiphar saw that the hand of God is upon Joseph. Thank God we can rely on His wisdom and strength to see us through our daily tasks. In all our accomplishments we must learn to point people to the Lord. The last thing I want to note is the particular phrase which says he was a "goodly person", "wellfavoured." There is nothing wrong with being wellfavourd even by the unregenerate. In fact, we have a better chance at gaining an audience with them if we make ourselves presentable (e.g. make use of a breath mint). I heard a preacher once say: "If anything offends, make sure that it is only the Gospel that offends."