The word "ponder" here comes from a Greek word meaning "to throw together." Strange. You can almost think of a chaotic scene of things being tossed about, much like what happens when a hurricane hits. Things are strewn about the neighborhood. But that's not what is meant here. It gives the idea of taking what you have "kept in your heart" and go over and over those things and look at them from every angle. "Meditation" is a similar thought - think through what you know and consider what something means.
Mary heard a lot of things, not only from the shepherds in the context of our Daily Verse, but also what Jesus would say to her in Luke 2:49, "...Why did you seek Me? Did you not know that I must be about my Father's business." In verse 51 we read, "...but His mother kept all these things in her heart." Mary did something that is a healthy activity for every believer.
Pondering the things of God - look at what God has said "from every angle." Ask how the things you have learned from God can impact your life. How can you put these things into practice? Are you understanding what you've learned? Should you study other truths in God's Word and see how these truths can enhance what you already know?
Meditation, pondering, thinking through: all these words suggest a process that goes far beyond just "reading your Bible." Be like Mary and take what God has shown you and "ponder" these things in your heart and put them to practice in your life.