It is easy to become boring when you're playing Dungeons and Dragons. All it takes is for you to become comfortable with your Game Master's style and the system. Then you begin to develop a standard routine for dealing with the world about you. You march in a standard order; you interact with non-player characters (npcs) the same way each time you meet a new one; you choose to roll your dice instead of announcing your actions. Face it, you're in a rut and the game is dull as hell as a result.
As a Game Master when you realize this has happened to your game you'll probably find yourself staring at your notes and wondering where you went wrong. Should you have used music? What if you had used two Ogres and a Mindflayer instead of the Hill Giant? Maybe you should have sprung for that fifty dollar game mat and deluxe box of miniatures? Or maybe you should have stopped taking the easy way and started stretching your gaming limbs.
Your players take their lead from you. If you ask for dice rolls every time that some minor challenge comes along then they'll soon be calling for their own rolls. What to find out rumors in town? Roll a Knowledge (local) check. Trying to find food out in the wild? Roll a Survival. Do you want to ask that bar maid back to your room for a nightcap? Roll a Charisma check.
Do you see how boring that becomes?
To break up that monotony the first thing you have to do as a Game Master is to stop letting your players roll for everything and start asking them what they're actually doing. If they want to screw the waiter till he can't remember his own name then have them actually approach him and talk out the scene with you. You don't have to be graphic, but having that player actually think about what they're going to say and how they want to engage the situation takes it from a d20 roll to a memorable event that the player will talk about after the game.
In a recent session I had a new player. He was incredibly shy around so many new people and was really hesitant to get involved in the goings on of the game. Yet when they went to the inn to get rooms and he had a waitress flirt with him he got involved. He moved from leaning back into his chair to sitting on the edge and describing to me how he wanted to try and woe her. She was a throw away npc and he still remembers her name three months later because he had to think about what he was doing and that made her something special.
After the inn he understood how this game was played and didn't just ask for the d20 roll to determine his successes. Instead, like most of my players, he would begin any situation by telling me what he wanted to do and then we would work it out. Sometimes we rolled to determine success, but more often than not the way that success was determined was by talking out the interactions. Choosing to interact with the events of the game rather than mechanically determining results is the difference between a boring game and a memorable one.