When you raise issues with the President, try to come away with both that decision and also a precedent. Pose issues so as to evoke broader policy guidance. This can help to answer a range of similar issues likely to arise later.
There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.
Treat each federal dollar as if it was hard earned; it was - by a taxpayer.
One of your tasks is to separate the 'personal' from the 'substantive.' The two can become confused, especially if someone rubs the President wrong.
Be able to resign. It will improve your value to the President and do wonders for your performance.
Public servants are paid to serve the American people. Do it well.