Preaching the gospel is not only a command from Jesus, but we should want to share our joy with others. This does not mean going from house to house knowcking on doors and rudely disturbing residents. Rather we can share it with friends, family, and complete strangers naturally if religion is being discussed. What is the gospel? At Luke 24:47, Jesus says "And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem." The good news is that we can be saved if we turn to Jesus. Some people want to preach something beyond what Jesus said. This is dangerous, as Paul says in Galations 1:8 "But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed."! Bad news indeed for those that do! However, we need to preach the TRUE gospel freely. One easy way to do this is to buy "Chick" tracts http://www.chick.com/
very cheaply and distrubute them by leaving them, at a library, store, restaruant, etc. If a person is shy, they may not feel comfortable talking religion with others. Some people are not shy and have no trouble at all. Whatever your case may be, you can always help spread the gospel of salvation to other people!