A very good policy to apply to your daily life is to never say something about someone behind their back that you wouldn't say to their face. As Solomon says, "a bird of the air may carry your voice". Obviously, he doesn't literally mean this. However, he does mean that these things have a way of making their way to the surface. Eavesdroppers, snitches, in this day and age we even run the risk of "pocket dialing".
Solomon goes a step further, however. Not only should we not say a thing out loud, but even in your thought, you are exhorted not to curse the king. There is very good reason for this seemingly strange command. Namely, just as that which is out has a way of getting around, that which is inside has a way of getting out. In drunkenness, in anger, when sleep deprived, you are more than capable of speaking what's on your mind. But you can't speak a thought you don't have.
Control of the tongue is a very important concept in Christianity. Through James, God even tells us that if we can't control our tongue, our religion is useless (James 1:26). But the control of the tongue begins with the control of the mind. Let us therefore think only on that which is true, just, pure, noble, lovely, and of good report (Philippians 4:8). If it's worth praising, meditate on that. Everything else should be left to perish with the world.