I encourage my brides to use bouquet holders - even if they want the hand tied look. That is easy to obtain by creating a "mock" hand tie. I have many tutorials showing how to achieve this while giving your wedding flowers that much needed water source.
Flower food is as essential to extending flower life as water. Use the correct amounts as instructed on the label, or it's not going to be very effective. Don't overuse either. Too much won't hurt the flower, but it's simply a waste of product.
Allow the bouquet holder to "float soak" - meaning you don't force it under the water level to try and hurry absorption. It is very quick to sink on it's own and saturate the foam with no dry pockets that can form if you force the foam to take up water too fast.
Secure it in a weighted holder so that it doesn't topple forward when you start adding in the weight of fresh flowers.