Avoid Wedding Day Challenges

Have all of the men and children that will be wearing tuxedos try them on at least the day before the wedding.  (Potential problems: wrong shirts, wrong vests, no ties, missing cufflinks, hems too short or too long).
Make sure that your florist is aware of your photo starting time so that your flowers will be ready and available.  Also, ask if your florist will be staying to pin on flowers.  If not, let the photographer know.
Have maps available at your ceremony with directions to get to the reception site.  This will save you and your parents from having to give directions numerous times to many of the guests.
If you have a family member or friend acting as a videographer make sure that they have plenty of battery power and blank tapes.  Please ask them to coordinate with the photographer as to where they will be standing during the processional and the ceremony so that everyone can work together for the best photos and videos.  (Potential problems: Battery power used up on the pre-wedding festivities and runs out during the actual ceremony, Video camera operator does not check with photographer and is visible in all of your photos)
You may consider having your flower girl and ring bearer sit down at the end of their walk down the aisle rather than actually standing for the whole ceremony.  This is usually hard for young children to do and they often will run around, lay down, or cry during your wedding vows.
Make sure that the bridal veil is secure.  It is hard to enjoy your day when you feel like your veil is constantly about to slip off.  Also, when well-wishers hug you they will often loosen the veil.
The bride and groom should remember to face each other during their vows.  This way the congregation can see you both and so can the photographer!  This is much better than keeping your backs to everyone and saying your vows to the Pastor/Rabbi/Judge rather than to your soon to be spouse!  Also, when you light your unity candle try to remember to leave some space in between the two of you so that everyone can see the candle being lit. 
Consider doing a "unity sand" ceremony rather than a unity candle.  For this ceremony the bride and groom each pour sand into a vase from their own two smaller vases.  This eliminates the problem of keeping candles lit.
Only use an aisle runner if it is necessary.  Aisle runners rarely lay flat down the aisle - they often bunch up to one side of the aisle or the other and the wind can send them sailing!  People often trip on them during the processional, and they can be tough for the ushers to unroll which can resort in laughter from the congregation right before the bride makes her grand entrance. Consider having rose petals down the aisle instead.
When arriving at the location where you plan to "get ready" be sure to bring all of your essentials with you so that they are actually with you.  For example, don't plan on someone bringing your earrings to you, they may run late and you may have to delay your photography while you wait for one last item to be arrive.  (This actually happens to brides quite often).
Be sure that everyone is ON TIME for the photography.  You may feel that plenty of time has been allotted, but actually every minute of that time is needed.  Plan to arrive early.  Delegate errands to other people.  Also keep in mind that if other people are taking photographs of you during your formal photography session, that while we wait for them to take their photos you are losing out on time that was planned for your professional photographs.
A hair and makeup stylist is a great idea to have you look your best for photographs, but they seem to take longer than planned about 99% of the time!  So, plan to be ready 30 minutes before you really need to be ready and it’ll work out just fine!
Try not to get upset about things that may go wrong on the wedding day, or things that don't go exactly according to your plans.  These are the things that you will laugh about in the future when you look back on the day.
For summertime weddings, bring a cooler full of water bottles for the family & wedding party. 
Last of all, be sure to actually "enjoy your day".  Plan enough time to get ready leisurely,  stop and smell the flowers in your bouquet, sit down and enjoy a piece of your wedding cake, dance and have a great time.