The Federal Government should be the last resort, not the first. Ask if a potential program is truly a federal responsibility or whether it can better be handled privately, by voluntary organizations, or by local or state governments.
The Secretary of Defense is not a super General or Admiral. His task is to exercise civilian control over the Department for the Commander-in-Chief and the country.
Test ideas in the marketplace. You learn from hearing a range of perspectives. Consultation helps engender the support decisions need to be successfully implemented.
Visit with your predecessors from previous Administrations. They know the ropes and can help you see around some corners. Try to make original mistakes, rather than needlessly repeating theirs.
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.