"Day-to-day" refers to parts of life that happen everyday, or nearly everyday, particularly if part of a routine. For most people in industrialized countries, going to work is day-to-day. For most people with good dental hygiene, brushing their teeth is a day-to-day experience. "Day-to-day" can also be used generally to refer to the routine portions of life.
Sometimes has a negative connotation when less routine and more excitement is desired.