We often have tacit assumptions about what students should do to be successful in our classes: take notes during lecture, ask questions, get started on the homework early, come to office hours, and read the book. These things might be different in each of their classes and some students might be better prepared to guess what the right things are. Help remove the guess work for students by making these expectations of their behavior explicit.
Example: "Start homework early so you have time to get help!"
See this and related tips as a Tip Sheet: http://csteachingtips.org/tips-for-reducing-bias