James 4:7

So submit to (the authority of) God. Resist the devil (stand firm against him) and he will flee from you. 

Take a stand against the enemy. Stop the thoughts when they start and use the authority Jesus has given you to make him leave. Speak against what he is trying to say and repeat the word to him. Jesus gave us power and authority, and whatever we bind on earth will be bound, and whatever we loose on earth will be loosed.