The first thing all presidents should do is faithfully execute the laws of the United States. That means a president must enforce them as they are, without selective application, ignoring those he may dislike, or declaring new meanings in those he may want to read differently. He must stay within the boundaries set by the law. Presidents after all are executive officers, not legislators. They are to do as congress instructs, and nothing more.
Were I president, that would be the first directive to all members of the executive branch. Anyone officer or employee who overstepped his authority and did otherwise would be fired and perhaps prosecuted.
That alone would make a vast difference in the conduct of the federal government. I wish there were a candidate on the ballot now who would do it. Unfortunately, there is not.