Catch the important moments for the bride and groom, the brie's entrance, the groom seeing the bride for the first time in her gown, the vows. If it is a Catholic Mass with Communion, take the Communion line. Our professional videographer filmed DH & I during the whole Communion part, and I would have mucch rather seen who was at the church, and coming up for Communion. Take the stuff the bride and groom won't see.
At the reception, circulate, circulate, circulate!!!!!!!!!!!!!!!!! Get the guests, get a lot of candid shots. Get the bride and groom doing the important stuff, but get candids. My friend also videotaped our wedding (in additoin ot the pro) and she got video of my DH's friend, a bit tipsy, slipping off the head table dais (our head table was elevated) and then slowly pulling himself back up to a standing position, all the while waving at the camera saying "I'm all right". It is a hysterical piece of footage!!!!