Choosing the right bouquet holder is important. You can choose a more decorative holder like the Elegant Bouquet holder, which has a built in wick in the handle.
An excellent choice for a cascade is using a Belle slanted handle, which allows for a more comfortable posture in holding the handle. I like the Grande, because that many flowers need a lot of foam support that can hold a substantial amount of water.
Begin by allowing the holder to rest in water that has had a flower food additive, taking care to follow the mixing directions. Using too much won't hurt the flowers, but it simply wastes product. Not enough really doesn't extend the flower life very much. These products have been developed over years of research and are much better than a "home remedy" of sugary soda that you make a guess at amounts needed.
You have a lot of investment in your wedding flowers - don't skip a few valuable fresh flower products that are really essential to extending the life of your flowers.
Always secure your bouquet so you can design hands free. You can use a narrow neck vase - just be sure it is well balanced and weighted down with marbles or rock. Flowers and wet foam can be heavy and you don't want the flowers to topple forward. This could cause bruising or creasing on petals that will show up by your wedding date.