Be not conformed to this world
Romans 12 v 2
It's hardly surprising God says this seeing He tells us friendship with the world is enmity with God, and if any man love the world, the love of the Father is not in him. We must be careful we don't misunderstand what God is saying here. It's not that we are to be negative about everything in the world and dismiss everything that is secular. There are many beautiful things to be enjoyed in nature and many activities that are not displeasing to God. God has given us many good things to enjoy in this world. We need to judge everything on its own merits in the light of God's word.
You see what you think is worldly may not be to another person. Not being conformed to the world has to do with the world without God. The worlds thoughts, aims, principles, practices, hopes and pleasures that are contrary to the will of God. The world doesn't take God into consideration in all these things but the believer in Christ does because we don't want to live contrary to the will of God.
It's not just not living by the standards, aims and principles of the world apart from God. It involves us being transformed by the renewing of our minds by the Holy Spirit through God's word. So the life of the believer in Christ is not formed by the world without God but by the will of God revealed in His word.
We need to also remember that things in the world that are good and legitimate become wrong when put before God in our heart's and lives. Deuteronomy 10 v 12, if put into practice will prevent us being conformed to the world, "What doth the Lord thy God require of thee, but to fear the Lord thy God, to walk in all His ways, and to love Him, and to serve the Lord thy God with all thy heart and with all thy soul."