Your Question: How do we apply the Bible in our lives today? Should we only apply the New Testament and not the Old Testament? People seem to apply the Old Testament according to their own ideas, ie tattoos and wearing earrings, forbidden in the Old Testament.
The Old Testament is certainly relevant for our everyday lives, the Christian Church and the New Testament are both founded upon the laws of the Old Testament. Jesus said “Do not think I have come to abolish the Law or the Prophets; I have come…… to fulfil them” Matthew 5:17. The law against tattoos, and markings on the body are made in Leviticus 19:28. Some people would say that this was in the context of cutting your body for the dead, and so justify having them, but the tattoo statement comes after this, so it would be wiser to refrain from having tattoos, if you have any reservations on it.
In the New Testament, Paul teaches that where there is some doubt it is better to refrain from doing something if it may cause a fellow Christian who is not so strong to stumble in their faith (1 Corinthians 8:13, Romans 14:21). The ten commandments are definitely the basis for living the Christian life, as the Jesus explained that all the laws of the Old testament are summed up in the words, “Love the Lord your God with all your heart, soul and mind, and your neighbour as yourself”” (Luke 10:25).
Wearing of Earrings is not actually forbidden in the Old Testament, but at times when people had sinned, or desired to deny themselves in order to draw close to God they took off their earrings (Gen 35:2- 4, Ex 33:5). There are a couple of references to earrings, that give a positive slant on earrings: Prov 25:12, Ezek 16:12, but again, whatever we do, even in wearing clothes and jewellery we need to do everything in order to glorify God. If you have doubts about things, it is better not to do them, than to go against your conscience, or cause another to stumble.