Make sure that all wedding party members and FAMILY know the photography schedule. For many people a 1:00 ceremony means they don't have to be there until 12:40. What they may miss is the fact that pre-wedding portraits were scheduled for 12:00. Failure to communicate this to them could mean that photographs scheduled to be taken before the wedding now have to be taken after the wedding. This takes precious time away from the reception and the guests.
Encourage all wedding party members and families to not plan their schedule to tight. For example, let's say that your grandparents know that the wedding is at 1pm. They may back into that "deadline" with planning like 10 minutes travel time, 15 minutes to get dressed and 10 minutes to have a shower. So in their mind they may think that starting to get dressed at noon would be fine. Planning this tight makes no allowance for travel delays, parking, that stubborn cuff link, or finding the wedding venue.
Hair and makeup can often take up to 40 minutes longer to do than what the make-up artist estimates. What they often miss in their planning is the social factor of a group of excited ladies before the wedding. If that time slot is overrun the rest of your wedding day schedule may have to slip, including the start of the wedding. Allow at least 30 minutes more than the plan if not an hour. If everything stays on schedule you will simply have a little more time for photography or relaxing.
Are you having a limo? Is all photography being done before or after the wedding? If you are not having photographs done before the wedding then you need to allow time for the photography after the wedding. Most professional photographers will take 30 minutes after the church is empty. If your wedding is at 6:00 and the ceremony is 20 minutes the photographer will be starting around 6:30. Don't schedule the limo until 6:45 or 7:00 at the latest.

Make sure that your florist knows the photography schedule. Unless otherwise told some florist may think that a one hour prior to the ceremony delivery is sufficient. Not having the flowers can really delay the wedding photography. While talking about florist, don't forget to order a throw away bouquett.

Always be sure to allow some extra time for yourself. Your wedding will be very rare one if it stays on schedule. You and your groom are the most important people that day. A few minutes here and there of being off schedule is a small trade off for enjoyng the first day of your new lives.