God Himself said in the beginning of the Bible:
You must rule over it... -- Genesis 4:7 (ESV)
... and not "obey" it as Paul said:
Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey,
- either of sin, which leads to death,
- or of obedience, which leads to righteousness
-- Romans 6:16 (ESV)
However, even believers may fail as Solomon said:
Surely there is not a righteous man on earth who does good and never sins. -- Ecclesiastes 7:20
So, how should believers rule over sin?
The fear of God may be before you, that you may not sin. -- Exodus 20:20 (ESV)
There's only one way that Israel's sin and guilt can be completely forgiven:
They must crush the stones of every pagan altar and place of worship.
-- Isaiah 27:9 (CEV)
“Repent, and turn from all your transgressions, so that iniquity will not be your ruin. Cast away from you all the transgressions which you have committed, and get yourselves a new heart and a new spirit. For why should you die? For I have no pleasure in the death of one who dies,” says the Lord God.
“Therefore turn and live!”
-- Ezekiel 18:31-32 (NKJV)
Blessed is the one whose transgression is forgiven, whose sin is covered.
Blessed is the man against whom the Lord counts no iniquity, and in whose spirit there is no deceit.
-- Psalm 32:1-2 (ESV)
David also witnessed:
I acknowledged my sin to you, and I did not cover my iniquity;
I said, “I will confess my transgressions to the Lord,” and you forgave the iniquity of my sin.
-- Psalm 32:5 (ESV)
Once, you had confessed your sin, you need to get baptized into Christ Jesus.
Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. -- Romans 6:3-6 (ESV)
When study and live according to God’s Teachings (Psalm 119:11, Psalm 1:2, John 8:32), then you will be able to recognize and refuse evil advice (Psalm 1:1).
God blesses those people
- who refuse evil advice and
- won't follow sinners or
- won't join in sneering at God.
Instead, they find happiness in the Teaching of the Lord, and they think about it day and night.
-- Psalm 1:1-2 (CEV)
(Note that "Teachings" comes from the Hebrew word "Torah" which is also sometimes translated as "word", "commands" or "laws" in some bibles.)
Often people will excuse themselves:
"I'm only watching (bad movies/games/pornography/etc.)" which implies that they believe that as long as they do not participate in the action they are observing it is still okay.
"It is just a (movie/game/music/etc.)" which implies as long as nobody gets hurt in real life it is okay.
"It won't hurt to know" which implies that all knowledge is safe.
But, God instructed us to avoid the knowledge of evil (Deuteronomy 29:29, Genesis 3:5-7) so that we do not fall into temptation (Matthew 18:7).
Even if we were raised in a home where the parents did everything to hide us from the "knowledge of evil", we were all still born with the knowledge of good and evil (Genesis 3:22) and temptations are everywhere and easy to find and hard to overcome.
Watch and pray that you may not enter into temptation. The spirit indeed is willing, but the flesh is weak. -- Mark 14:38 (ESV), Matthew 26:41
However, there is hope for converted believers:
For because he himself has suffered when tempted, he is able to help those who are being tempted. -- Hebrews 2:18 (ESV)
Paul witnessed that God is not evil:
Blessed is the man who remains steadfast under trial, for when he has stood the test he will receive the crown of life, which God has promised to those who love him. Let no one say when he is tempted, “I am being tempted by God,” for God cannot be tempted with evil, and He Himself tempts no one. But each person is tempted when he is lured and enticed by his own desire. Then desire when it has conceived gives birth to sin, and sin when it is fully grown brings forth death. Do not be deceived, my beloved brothers. -- James 1:12-16 (ESV)
Therefore, God will always provide a way to escape our own desires.
No temptation has overtaken you that is not common to man. God is faithful, and he will not let you be tempted beyond your ability, but with the temptation he will also provide the way of escape, that you may be able to endure it. -- 1 Corinthians 10:13 (ESV)
Don’t sin by letting anger control you. Think about it overnight and remain silent. -- Psalm 4:4 (NLT)
Even Jesus got angry, but he was not out of control. He was focused on his task to cleanse the temple.
In the temple he found those who were selling oxen and sheep and pigeons, and the money-changers sitting there. And making a whip of cords, he drove them all out of the temple, with the sheep and oxen. And he poured out the coins of the money-changers and overturned their tables. And he told those who sold the pigeons, “Take these things away; do not make my Father’s house a house of trade.” -- John 2:14-16 (ESV)
John, the Baptist, also got angry, but in his anger he firmly warned the Pharisees and Sadducees of God's judgement that will come upon them.
But when he saw many of the Pharisees and Sadducees coming to his baptism, he said to them, "Brood of vipers! Who warned you to flee from the wrath to come? Therefore bear fruits worthy of repentance, and do not think to say to yourselves, ‘We have Abraham as our father.’ For I say to you that God is able to raise up children to Abraham from these stones. And even now the ax is laid to the root of the trees. Therefore every tree which does not bear good fruit is cut down and thrown into the fire." -- Matthew 3:7-10 (NKJV)
If you find it hard to control your words, rather stay quiet as David did:
I said, “I will guard my ways,
that I may not sin with my tongue;
I will guard my mouth with a muzzle,
so long as the wicked are in my presence.”
-- Psalm 39:1-2 (ESV)
The one who conceals hatred has lying lips,
and whoever utters slander is a fool.
When words are many, transgression is not lacking,
but whoever restrains his lips is prudent.
-- Psalm 10:18-19 (ESV)
The apostles also understood that...
If anyone thinks he is religious and does not bridle his tongue but deceives his heart, this person's religion is worthless. -- James 1:26 (ESV)