Leave the President's family business to him. You will have plenty to do without trying to manage the First Family. They are likely to do fine without your help.
Don't begin to think you're the President. You're not. The Constitution provides for only one.
Walk around. If you are invisible, the mystique of the President's office may perpetuate inaccurate impressions about you or the President, to his detriment. After all, you may not be as bad as they're saying.
Don't automatically obey Presidential directives if you disagree or if you suspect he hasn't considered key aspects of the issue.
See that the President, the Cabinet and staff are informed. If cut out of the information flow, their decisions may be poor, not made, or not confidently or persuasively implemented.
Many people around the President have sizeable egos before entering government, some with good reason. Their new positions will do little to moderate their egos.
Preserve the President's options. He may need them.
Know that the immediate staff and others in the Administration will assume that your manner, tone and tempo reflect the President's.