If we pay attention to what He says, and do what He tells us to do, we can be absolutely certain that we're doing the right thing. There would be a lot less uncertainty in our lives if we paid more attention to God's divine directives.
Along with a knowledge of His directives, we need the good sense to D0 what He directs us to do. Many of God's directives hold great promise of divine blessing to encourage us to obey them.
A typical example is the threefold directive you will find in Proverbs 315-6. "Trust in the Lord with all thine heart; and lean not unto thine own understanding. In all thy ways acknowledge him, and he shall direct they paths."