The devil takes great pleasure in deceiving the people of the Lord. Russ Dizdar refers to it as "voice to skull technology" where demons will literally throw thoughts into your mind. We need to study the Bible in order to know the true revelation vs demon inspired thoughts and ideas. As in 1 John, we need to test the spirits. We also need to understand our authority in Christ and should be rebuking and casting out any demons that could be influencing our lives, daily!
In order to truly understand spritual warfare, you first have to understand that the idea that a Christian can't have a demon is a false doctrine. Many people do not get the deliverance they need from demonic influences because of that false doctrine. Sometimes the Lord will leave a demon in a Christian in order to teach them spiritual warfare when they are ready. Sometimes a Christian will bring it on themselves by willful disobedience and when they repent, and turn back to the Lord again, they need deliverance. Many Christians are on anti-depressants and various other drugs because they believe that Christians can't have demons, when the Christian could be under the influence of spirits of depression and spirits of opression that they need to be delivered from. It is the first step in spiritual warfare.
The realm of spiritual warfare is too big for me to cover in this posting, but I want to give some resources
Russ Dizdar of Shatterthedarkness.net has hundreds and hundreds of mp3's that address spiritual warfare topics. He has a class called Confronting the Powers that is being offered free on his site that I highly recommend.
Confronting the Powers
The Word tells us NOT to be ignorant of Satan's devices. David Eells of Unleavened Bread Ministries also has some great mp3's on this topic. Some I believe that directly address this topic are here:
What spirits do you follow?
He also has another one called Demon Tactics.
But the best resource of all is our Heavenly Father. If you have questions about whether or not WHAT you are listening to is from Him or some other spirit, He will answer you if you seek Him diligently.
Dear Heavenly Father, thank you for the blood and name of your son, Jesus Christ, Yeshua, that gives us authority over the spirit realm and the gates of hell shall not prevail against us. Thank you so much for the great deliverance you give us each and every day. In Jesus name. Amen.