My best advice is to learn as much about your chosen religion as possible. Learn it from the inside out, as best as you can. I know that sounds almost impossible, but be able to answer any questions anyone could ask you, especially the tough ones. If it makes you uncomfortable to confront them, then simple practice normally. Once they see how fulfilled you are, how happy you are, how it improves your life in all aspects (such as school or work, or with friends, or within yourself) then they'll start to open up their minds to talking about it. Being aggressive about it will only make them that much more combative. Be understanding, and most of all, don't judge and don't accuse. Just try and speak from your heart.