If possible, get either the bride or the groom to wear one, and get the minister or celebrant to wear one. This way, you'll have crisp, clear sound. Technical skills are important, but they can be learned. The most crucial skills are smooth panning and zooming. Before you ever do your first PAID wedding, practice with another event - for free.
Practice makes for fluency.
People look around when they're at a wedding, and so should the camera, within reason. Practice a slow, smooth pan that keep the subject in the frame of the camera. Practice smooth zooms that aren't jerky, and aren't too close or too far from the subject. You've probably figured that you'll need a helper for the actual taping. Unless the only camera that will pan and zoom is the one you're operating, and the others are stationary, you'll need someone.