Most people today who have any concept of idolatry probably think of pagans bowing down and worshipping a strange-looking idol—a carved image or statue. That's part of what idolatry means, but since most of us today don't do that, how do God's commands against idolatry apply to Christians now?
In the King James Version of the Bible, there are three different words translated as "idolatry." Each one (teraphiym, kateidolos and eidololatria) has at its core the concept of serving or worshipping something other than the one true God.
The apostle Paul provides us with a modern application of idolatry in the middle of a sentence in his letter to the Colossians. He mentions "covetousness [greed, New International Version], which is idolatry" (Colossians 3:5).
So idolatry is not just venerating a statue, carving or painting. Idolatry occurs when we begin to value anything more than we value God. If we spend more time thinking about our hero than God, that's idolatry. If our every thought is about the latest gadget or our personal appearance, that's idolatry. If the first priority in our lives is our family, even that's idolatry.
When God said, "You shall have no other gods before Me" (Exodus 20:3), He wasn't just talking about the imaginary deities that seem so ridiculous to us today. He was talking about anything that usurps His place as number one in our hearts. The solution to this problem is as simple (and as difficult) as Christ's admonition in Matthew 6:33: "Seek first the kingdom of God and His righteousness."
Everything else must come after.