God tells you how to fight Satan. God says you should bind all evil spirits out of your mind and put on God's Armor. Then pray a hedge of protection around yourself. God will do the rest. Once you are saved you are God's child and wants you to know who you are in Christ. God says you are His child and you are more than a conqueror. He says you are an ambassador for Christ and you are to fight the evil around you. He also says you can do all things thru Christ and that all things are possible if you believe. So trust God and use His might to strengthen yourself.
Your mind When you got saved you received a new spirit. That spirit is perfect and wants to please God. However your mind is not new, you have the same mind you had when you were a sinner. And so God says your mind has to be transformed by reading the Word of God Rom.12 Do not conform to the pattern of this world, but be transformed by the renewing of your mind. with the Word of God. Satan knows that your mind is still the same so he try's to attack your mind. The battle ground here on earth is for the control of your mind. The only weapon satan has is to attack you thru your thoughts. He tries to discourage you by telling you about all of your failures, sins, wrong choices and bad relationships you have had. He wants to take control of you by controlling your mind. He has no power so he uses deception and lies to try to deceive you.
2 Timothy 1:7 7 For God has not given us a spirit of fear, but of power and of love and of a sound mind. Philippians 4:13 13 I can do all things through Christ who strengthens me.