Isaiah 26:3 Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee.
Exhortation: Joan Boney
Staying our mind on God is focusing on that which God shows us about the issue at hand. (Dreams, scriptures, thoughts from Holy Spirit) When we believe we have heard from God and refuse to allow ourselves to think of things other than that which we believe God has shown us, then we live in perfect peace.
Many thoughts contrary to that word will come to our minds. But we keep remembering what we believe God has said about that subject and we reject all other thoughts.