Apparently the wise man will take time to be quiet and listen. Ultimately, God can get our attention if He wants to but this simple prayer for God to guard our mouth will save a lot of grief. Someone has wisely noted that when in doubt, be quiet and listen. Listening is an important skill as someone noted: God gave us one mouth and two ears so we would listen twice as much. There is another cliché that goes, "Some people have something to say, and other people just need to say something." The point is that all of us need to spend more time silent so God can talk to us through His word and then we can listen to what He and others are trying to say to us.
The Psalmist continues his prayer is verse 4 asking God not to let his heart be drawn to what is evil and not to take part in wicked deeds with men who are evildoers; "let me not eat of their dainties" (delicacies). The Psalmist is calling attention to the fact that we as human beings are easily drawn away from God to do the wrong thing. One reason people are compared to sheep in the Bible is that sheep easily turn away from where they should go. It takes a shepherd to constantly keep the sheep traveling the right direction.
The verse is making a statement that without God's guidance, it is very easy for any of us to wander away from God and what He desires for our lives. The related point is that evil deeds do exist in this world whether we accept it or not. We can't fix this world, but we may choose to get away from where we know God does not want us to be at moment.
The "dainties" or delicacies mentioned at the end of verse 4 probably refers metaphorically to illicit sacrificial offerings and pleasurable acts of sin. Yes, sin can be pleasurable but only for a season (Hebrews 11:25). Therefore, pray for God's protection to keep you from sin in your life.