Jesus began His ministry at the age of 30. Before that, little is known of Him, except that He lived in Nazareth, with His family. When He began His ministry He went south, and was baptized and then went into the wilderness to be tempted. Very soon after this He went back to Galilee, and for the most part spent the first year there preaching and teaching in the area of Galilee, and going to Jerusalem for Passover.
In the second and third year of Jesus’ ministry He was almost exclusively in Galilee, the northern part of Israel. During these years, He was only going south for the Passover and other feasts. The last few months of Jesus’ ministry were spent in the south, finishing in Jerusalem, when He made the triumphal entry into Jerusalem, taught in the temple, held the Passover (the Last Supper with His disciples), went to Gethsemene, was tried, convicted, crucified, buried and rose from the dead.
So all in all, Jesus preached about three years.