Pick up the Little Blue Book and other printed daily reflection books in church.
Online Resources:
Advent Resources from Catholic Climate Covenant - include the Advent Simplicity Challenge, Praying with Catholic Relief Services Advent Wreath, Candle Lighting Litanies, and more
Advent Calendar for Adults from Loyola Press - daily video and written reflections
Dynamic Catholic - Best Advent Ever with Matthew Kelly - sign up for daily emails
Advent Resources from the United States Conference of Catholic Bishops (USCCB)
Hallow - #1 prayer app; get 30 days free for tons of Advent resources