2Co 10:5 Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ.
Everyone has temptations to meditate on evil.  

Even the holiest person on this earth has temptations to meditate on unrighteousness

The battle between God and Satan is for your mind. Once a particular thought has been entertained over a certain period of time, the thoughts will eventually result into actions. The character of a person is the direct fruit of his or her own thoughts.

We are supposed to take care of what we think because our thoughts will eventually influence our character and cause benefits or harm to us and to our brothers and sisters in the society.

The word of God instructs us to cast down every thought that arises against the knowledge of God and bring every thought to the obedience of Christ.

Thoughts that are against the knowledge of God are sinful thoughts such as lust, lies, theft, murder, vile affections, et cetera. If the wicked one wants you to fall into transgression, he will first of all make you think about the sin. It is impossible for a person to fall into sin without first of all entertaining the sinful thoughts.

That is why a lot of people are bound to pornographic films, masturbation, stealing, hatred, strife, et cetera, because they fail to suppress thoughts of wickedness that are projected by the enemy right out of the gate.

For example, when a man or a woman commits adultery, that means that thoughts of lust were entertained before the sexual sin was committed. Jesus knew that if you can suppress sinful thoughts in your heart, you will avoid falling into sin because the wicked thoughts are suppressed before they are born.  

Once you make it a habit of thinking good and beneficial things which are pleasant to God, the thoughts will result into righteous acts that bear good fruits for the glorious kingdom of God.

Pure thoughts manifest into pure actions while evil thoughts manifest into evil actions. You are what you think. The word of God tells us, as a man thinks so is he.

The following are some of the ways in which we can use to overcome evil thoughts.

Do not watch or listen to profane media.
The music, the movies, the television programs that are displayed today in this evil and adulterous generation promotes sexual immorality and perversion. Avoiding worldly movies, worldly music and unholy television programs is a good strategy to blocking evil thoughts from entering your mind.

Bouncing off your eyes.
Bouncing off your eyes can be applied in any situation where you encounter an image that is lascivious and capable of triggering evil thoughts. For example, if you walk down the street and satan walks in front of you a lewd woman with the spirit of seduction, you are to bounce of your eyes and look in another direction until the woman leaves.

Bouncing off your eyes can be applied in major highways where there are obscene images and anything that is capable of triggering evil thoughts

Resisting them.
Evil thoughts are bound to come. We as Christians are expected to resist evil thoughts with the help of the Holy Spirit.
Once a thought has been projected by the enemy, we are to resist the thought and force our minds to focus on things that are worthy of praise, such as meditating on a particular scripture. Resisting evil thoughts is a habit that is mostly done by mature Christians.

Rebuking them.
The devil in several occasions forces evil thoughts into our minds. In such cases you can rebuke the thoughts in your heart or verbally in the name of Jesus. The devil speaks to us through thoughts. He causes us to sin by projecting evil thoughts into our minds. We as Christians are expected by God to think on good and beneficial things which are worthy of honor.

Once you develop the habit of resisting evil thoughts and bringing every thought to the obedience of Christ, you will find yourself having pure thoughts most of the time and evil thoughts would be rare as they are suppressed as soon as they are projected by the enemy.

Remember the battle is for your mind. The life that you live is the direct fruits of your own thoughts.
How to overcome evil thoughts.
Comments or Questions.

Biblical teaching on lasciviousness.
Hell is a real place.
Should Christian women wear high heels?
Modest dressing for Christian women.
Should Christian women apply make up?
How demons enter our lives.
Attires of harlots.