As others have said, let people help you. But when people DO help, be sure to be gracious (my soror big sister, do i have to specificy greek here, i'm so used to doing it for non greeks
just got married and my boyfriend helped a TON, since he wan't in the wedding party he was able to run a lot of errands - however he was VERY hurt that he was not thanked at the rehearsal dinner, but he loved that the mother of the bride hugged him about 100 times telling him how indispensable he was)
take time to enjoy yourself, things will go wrong, but if you stress too much, you'll never enjoy any of it.
If it rains, or looks like it will rain, forego any outside pics
(this may seem obvious, when above mentioned sister got married she was insistent on outside pics at a park and got caught in a rainstorm)
when something like that does happen, let your bridesmaids put your hair back together and go out there smiling
Hmm, don't make the rehearsal dinner longer than it has to be - no one in your bridal party is an idiot, and they can probably figure out how to walk down the aisle in less than 10 practices (yes, this has happened to me) This is especially true if the building has no air.
From the twice maid of honor perspective, I think that's it.
have a gorgeous wedding day!