Human life on Earth is subject to opposing powers: 

God

• Defined by the essential characteristic of omnipotence (ultimate power)
• Loving by nature
• His Will is a state of eternal perfect truth, peace and harmony (Heaven)
• As a consequence of His loving nature, He endows man with free will rather than exerting absolute control over man, even though it is within His power to do so
• Free will allows individuals the ability to choose to align their will with God, or to oppose His Will and rebel against God (sin / evil)
• The existence of evil at a holistic level is therefore within the ultimate scope of God's Will.   Freedom is risky, but God thinks it's worth the risks.
• Tends not to reveal His presence or influence to man in any way that would convince man unequivocally of God's actual existence, power and nature, because armed with such knowledge man would be sure to choose to align his own will with that of God, thus rendering the choice a product of coercion rather than of free will. 
• Therefore, God tends only to reveal His presence and power to man via miniscule hints that suggest His presence, but leave a sufficient degree of doubt possible to the reasoning mind of man so that his free will is preserved.
• Without a sufficient degree of opposition to God's own Will, man will have no opportunity to make a free will choice to align his will with that of God, so God requires that an opposing force of sufficient power, influence and intelligence be introduced into the equation.

Satan

• A created being according to Bible doctrine
• Ultimately subordinate to God at the holistic level, therefore not co-equal
• Exercised his own free will choice to defy God's Will and attempted to elevate himself to the status of God.  This fulfills God's need for the existence of an opposing force, and God therefore grants Satan significant influence in worldly affairs. 
• Seeks to rule and dominate man, but must operate within the constraint of respecting each person's free will just as God respected his. 
• To maximize his power over humanity, key areas of operation for Satan are government, banking and religion.
• Extreme degrees of pressure, torment and influence can be brought upon man in an attempt to obtain man's free will choice to surrender to Satan, so long as the pressure is not so great as to leave man no other choice, which would be a free will violation (see Job).
  
• Most rational men would not knowingly make an explicit choice to give up their freedom, therefore Satan must be an excellent salesman and "seal the deal" using any and all means possible, and he must convince man that such a decision is something other than what it actually is
• Deception is therefore the fundamental tactic, upon which all other tactics and operations will be built.
• 100% deception would constitute a fraud, and therefore a free will violation.  Since God's law requires Satan to respect human free will, Satan may create a pervasive environment of deception, but somewhere within there must always be a disclaimer of truth in order that free will is not actually violated.  Satan will minimize such disclaimers as far as possible ("the fine print,") but they must nevertheless be present.   Therefore, if man decides to ignore the warning and purchase Satan's bill of goods, he can be held accountable for having made an informed choice. Satan's disclaimers in the midst of deception may take any form, and no two situations will be alike -- they will be tailored to the individual person and their situation -- just as God's "hints" described above are.

Major Tactics of Satan

• Appeal to man's doubts concerning the existence of God.  If man doubts the existence of God and perceives Satan as all-powerful, man will conclude that it would be foolish to oppose Satan and therefore will submit to his domination (cults, organized crime, totalitarian governments).
• Appeal to man's doubts concerning the existence of either God or Satan.  If man doubts the existence of non-human powers, and believes man is the highest form of intelligent life, he can be led to deify his own God-given faculty of reason, which Satan can then use against him.  Reason and logic absent from God can be used to convince man that Satan's will is the rational, logical and in fact obvious choice (atheism, communism).   
• Appeal to the yearning of man to be closer to God by masquerading as the agent and steward of God ("an angel of light" as the Bible puts it).   If Satan can convince man that he is not actually Satan but is in fact God, he can then encourage man's natural inclinations toward good in areas of no importance to gain credibility, then use that earned trust in an attempt to influence and divert man's key decisions in areas that do bear upon Satan's goal of co-opting men's free will (some organized religions and quasi-religious organizations).

 The Bible

The Bible consists of several dozen books and letters that were written by human beings who, in some cases, claimed to be under the divine inspiration of God.  Some of these books, particularly those of the Old Testament, document the laws, customs and other practices of ancient people related to their religious worship, many of which seem to have nothing to do with a God that is decent or just.  For example, certain Old Testament books call for the execution of people by stoning or burning at the stake for things we that wouldn't even consider crimes today, such as cursing one's parents or breaking the Sabbath.  

Many religious people today, having succumbed to Satan's influence, will tell you that God Himself requires you to follow these rules, but Jesus' own words show them to be deceivers:

Satan, however, will seek out susceptible types of people who do not understand Jesus' message and convince them that, simply because these ancient customs were recorded in what they have been taught to call "God's Word," it follows that God must want people to follow all of those laws today! Satan will inflate their egos and senses of self-righteousness, and try to get them to enforce these laws on others.  This is called legalism (1) (2), and is a trap that people from many different religious backgrounds fall into.  Here is one example from a news clipping dated October 2012:

Satan teaches these susceptible people that they need to blindly accept these ancient religious texts as "God's Inerrant Word," and that it is literally true in every respect, no matter what truths God otherwise may be trying to put into their hearts today. Satan hopes that these people will stay fixated on the dead letters of these ancient, often-barbaric texts and never realize that, by doing so, they have closed their hearts to God and shut Him out from communicating with them directly -- in the present!

Not that we are sufficient of ourselves to think any thing as of ourselves; but our sufficiency is of God; who also hath made us able ministers of the new testament; not of the letter, but of the spirit: for the letter killeth, but the spirit giveth life. (2 Cor. 3:5-6 KJV)

Indeed, rather than attempt to follow the teachings of Jesus and emulate His behavior, many people today, including a large percentage of those who outwardly profess to be "Christians," find it easier to just attend their particular religious organization and ignorantly quote rules like the Pharisees did. Of course, they will pick and choose the laws that they think they can get away with forcing on others due to popular support, but ignore others when they are inconvenient. For example, even the most ardent legalist today will not usually try to convince you to put your children to death for disobedience, because they realize no rational person today would have the patience to listen to such nonsense.

But many of them will still fight devilishly hard for legalistic enforcement of ancient Sabbath-keeping rules (e.g., modern blue laws), or, let's not forget that old-time favorite, advocating hatred, intolerance, and outright violence against homosexuals.  But by doing so, they are still following the example of the Pharisees instead of the teachings of Jesus, even if they wear a cross on a necklace or have a Christian-themed bumper sticker on their car. These outward signs are meaningless and might impress their neighbors, but they do not fool God, who knows what is truly in their hearts (Matt 7:21-23, Matt 6:1-18, Matt 7:13-14). Many of these people never think very long about the fact that it was the Pharisees -- the religious authorities of the day -- who conspired with the government to have Jesus put to death.

But their minds were blinded: for until this day remaineth the same vail untaken away in the reading of the old testament; which vail is done away in Christ. But even unto this day, when Moses is read, the vail is upon their heart. Nevertheless when it shall turn to the Lord, the vail shall be taken away. Now the Lord is that Spirit: and where the Spirit of the Lord is, there is liberty. (2 Cor. 3:14-17 KJV)

See also: Galatians 3
See also: Commentary: Matthew 5:17-19 and "The Law"

In the above quotation from the gospel of Matthew, Jesus tells the religious legalists that they are "vipers" who are bound for the "damnation of hell" (Jesus's own words!)  You need to stop and think about this for a moment, and reflect upon whether Jesus might be trying to tell YOU something through this message. The fate of your soul may depend on it!

Satan's tactic of legalism can only be successful if he can get people to stop talking to God directly and praying sincerely for God's guidance in their lives.  For the trick to work, Satan needs people to believe that they already KNOW God's Will and that it is their job to enforce it on others. If he can get them to worship "every jot and tittle" recorded in the Bible INSTEAD OF ACTUALLY WORSHIPPING GOD HIMSELF, then Satan has got them firmly in his clutches. They are damned, while remaining the entire time totally convinced that they are warriors for God.

Satan will also find lots of people who didn't fall for the religious legalism scam.   When he approaches these people, he will very cleverly use the opposite approach and say, "look at those religious fundamentalists, trying to impose their beliefs on everyone else.   They are obviously very dangerous, violent and backwards people for believing what they do.    If there is a God and He is just, He would not be promoting these horrible doctrines.   It is clear that this whole business of people believing in God is an outmoded idea that has no place any more in this day and age.  Let us band together to stamp it out once and for all from the face of the Earth."   And many people, some quite intelligent, will agree with the logic of this argument and turn away from God entirely.   And they, too, will never realize that they have been tricked.

God does not personally appear to most of us in a cloud of fire, pointing His finger at us and instructing us "This is My Word and you must follow it!" The reason He does not do this is because He has given us the free will to make up our own minds.

Since Satan's purpose is to oppose the Will of God, he will do whatever he can to discredit God and sabotage God's work. Satan does not necessarily care if you believe in God or not as such; rather, he is more concerned with whether or not he can con you into working against God's Will, regardless of whatever religious or philosophical framework you are coming from.