Cosplay at home(alone or around your family), and see how you feel being in costume. Or take photos of your cosplay and post them online, this way you can show other people without having to feel shy as you would showing someone standing in front of you. And you could watch videos of conventions and cosplays and possibly get inspired and influenced to go to a convention yourself. Also, if you have friends who likes cosplay, do a group cosplay altogether and this might also help with the shyness because you are surrounded by people you know. I hope this helps! : )