I think you should be the way you feel comfortable with don't go with the social norms and change yourself for something that your not. Everyone is special in their own way and they may say your quiet at first but what you could do is if you want to build up a conversation would be to start by asking the person how was your day? Or complimenting what their wearing and build the conversation from there on.
If people need to tell you to speak more than they arent helping you feel comfortable around them. Be comfortable with your quietness, it doesn't mean you're boring. Maybe it just means that you haven't found people who share the kind of interests that make you feel excited and talk. The right kind of people often bring you outbox your shell. But at the same time there is nothing wrong with being quiet. It doesn't always have to be an uncomfortable silence. Just be the listening ear people need i suppose.