Sit by him at church. Smile at him when appropriate...make small talk or have a conversation with him. Make sure you flirt *a little*, play with your hair, your head...touch him briefly on the arm if he tells a joke. Actions always speak louder than words...SHOW him you're interested...
Relax, the more you talk with him the more comfortable you will become. Don't rush things, don't be unnatural. Whatever you do, dont' show too much interest too soon. You may scare him away.
If things are going to happen, they will.
Best of luck, sounds like you two are good kids.