There is something in each one of us that the devil can use. The devil could not tempt Jesus because sin does not leave in Him. The devil does not give us evil desires, he just exploit the weakness that already exist. James 1:14 But each one is tempted when he is drawn away by his own desires and enticed.
An idle mind is an undisciplined mind, a wondering mind. An idling mind become easy target to evil thoughts. Don’t let your mind wonder about thinking abound whatever it wishes. Philippians 4:8 Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy-meditate on these things.
Think about positive things.