It should be evident to anyone watching that a person is a Christian. Being a Christian entails being Christ-like; Paul wrote that we are to be "crucified with Christ," that is, dead to the flesh, and yet live—"not I, but Christ liveth within me" (Gal. 2:20). The Bible teaches us that once we have accepted the gift of the Holy Ghost we become a "new creature" (2 Cor. 2:8-9).
A Christian is holy, obeying the laws of God (Matt. 9:16-19). We are also to go "the extra mile" in our behaviors (Matt. 5:40-41), as well as being diligent and thorough in all that we do (I Cor. 10:31; Col. 3:23).
We are to care for the needy and unfortunate (Jam. 9:27). Jesus taught that the commandment to love your neighbour as yourself is second only to loving God (Matt. 22:37-40). John wrote that if you do not love your brother you are not of God (I John 2:9-11; 3:10-12; 14-17). This love precludes any form of bigotry (Jam. 2:9). We should seek to live in peace with all men (Heb.12:14).
Christians do not give place in their lives to the things of the flesh, nor are they friends of the world (1 John 2:15; Tit. 2:12; Jam. 4:4). We do not visit places that are home to immoral behavior, even to witness to sinners (1 Cor.15:33); furthermore, we are to avoid the very appearance of evil (1 Thes.5:22). We should not entertain sinful thoughts or attitudes; but rather think on things that will edify our hearts and minds (Philipians 4:8).
There are also activities that every Christian should participate in. Prayer (Rom. 12:12; Eph. 6:18; 1 Thes. 5:17), study of the scriptures (John 8:31-32; 2 Tim. 2:15; 2 Pet. 1:5), and witnessing to others (2 Tim. 4:2). We should attend church regularly (Heb. 10:25), and submit ourselves to a Man of God (Heb.13:17; 1 Pet. 5:5; Rom. 10:14; 1 Cor. 1:21).
Christians are modest in their appearance (1 Tim. 2:9; 1 Pet. 3:3-4); and should wear clothing pertaining to their respective genders (Deut. 22:5). Men should be masculine, and women feminine, in their demeanor and actions (1 Cor. 6:9); feminine men and masculine women, as well as the sin of homosexuality, are unnatural in God's eyes (Rom. 1:26-27).
While perfect holiness is not possible in this life, it should be striven for at all times, as it is essential to continuing salvation (Hebrews 12:14-15).