I have been crucified with Christ and I no longer live, but Christ lives in me. The life I live in the body, I live by faith in the Son of God, who loved me and gave himself for me. Galatians 2:20
The flesh is the part of us that resists our transformation into the new person in Christ. Our flesh wants to keep us enslaved to our old habits and sinful attitudes. We have daily choices to live according to the God's righteous desires, and deny sin. When we use our power to choose God's way instead of sin's way, we crucify our flesh.
God helps us crucify our flesh through the Holy Spirit (Romans 8:13) so that we may live in the "newness of the Spirit" (Romans 7:6 NKJV). The desires we must crucify include fornication, lustful passion, covetousness, anger, malice, blasphemy, filthy language and lying (Colossians 3:5-9). Paul noted that as we put these things to death, we are able to then put on the new man, "renewed in knowledge according to the image of Him who created him" (Colossians 3:10 NKJV).
Specific actions to take:
Some examples: If you know you'll be alone tonight and will be able to surf for porn on the net, invite a friend over so you don't have the opportunity to get into trouble. If you are headed to the beach and are prone to lusting after people in swimsuits, try going when there will be few people there, or leave your glasses at home (if you wear glasses), or just stay home. If you have trouble lusting over the magazine covers at the supermarket checkout, pick something to focus your eyes on in the checkout area that will keep you from looking at the magazine covers.
These may sound like extreme things to do. We have to do some extreme things when we're trying to break free from sex addiction. While in recovery, though, we must exercise discretion and not do things that will place temptation in front of our eyes.
Crucifying our flesh does not mean that our life will lack pleasure. God promises that we will drink from his river of his pleasures (Psalm 36:8). He is the author of true pleasure that is not tainted with sin in any way. He provides perfect pleasures that bring lasting satisfaction, unlike anything sin could offer. If we seek his Kingdom and righteousness first, he will take care of all our needs (Matthew 6:33).
Another helpful verse to remember:
Now those who belong to Christ Jesus have crucified the flesh with its passions and desires. Galatians 5:24