If you receive your bouquet in a box from a mail order company, keep the box cool until you can prepare the flowers. I really like the flowers you arrange yourself. Usually when we buy our flowers this way they are in really good shape and last a long time as well.
One of the first things you do when you get a bouquet home is to remove the rubber bands and trim the stems. Remove lower leaves and any dead leaves from the bottom of the stem to the water line of your vase so mold/fungi will not grow and infect the water and your flowers.
Lay a flower on a cutting board, with a sharp knife, cut the stems 1-2 inches from end of the stems at a slant, place the flower in water immediately. This opens the stem to receive the food and water. After a flower has been out of water for some time the stem seals shut, trimming the stem again will open it up again. Repeat with all your flowers.
Tip: Even if my flowers arrive in a vase of water I still take them out re-cut the stems and remove the water line and lower leaves.
Store bought bouquets usually come with a flower food packet attached to them. If you did not get one, here are some easy recipes to make your own.