They overcame him by the blood of the Lamb and by the word of their testimony. —Revelation 12:11
If we are going to do spiritual warfare, then we need to know Satan's tactics in order to overcome them. Satan is out to deceive. Revelation 12:9 describes him as "that old serpent, called the Devil, and Satan, which deceiveth the whole world" (KJV).
How does he set about his deception? In 2 Corinthians 11:14, Satan is called "an angel of light," which means that he uses apparently respectable means and people to deceive us. He tries to lure us away from the truth and towards the counterfeit. Paul says: "For if he that cometh preacheth another Jesus, whom we have not preached, or if ye receive another spirit, which ye have not received, or another gospel, which ye have not accepted, ye might well bear with him" (2 Cor. 11:4, KJV).
Satan is out to demoralize: "Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night" (Rev. 12:10, KJV).
How does Satan accuse? Sometimes he tells us that we are not saved. Or if he can't succeed with that, he tries to convince us that God has finished with us and that we are irreparably out of His will. Nothing is more demoralizing to a Christian than this. But let me give you a rule of thumb here: all oppression is of the devil.
Another method of accusing and demoralizing us is to tell us that we are not fit to worship God as we are. The devil reminds us of some weakness or failing in our life, and he says, "You must get that right before you can worship God. You're not in a fit state to do anything." He tries to get in during the week, and if he fails there, he tries on Sunday morning. If we lose our temper or give in to some other weakness, he says to us, "You see, you're not fit." But God never says that.
So what are we to do in the face of Satan's strategies? The answer is that we must refuse to give place to him. We must realize that Satan's strategy is aimed to produce one thing—a grieved Holy Spirit. That is all he wants. And if he achieves that, then he has won.
Excerpted from Worshipping God (Hodder & Stoughton, 2004).