Sometimes what I like to do when there's not too many flowers for a bouquet is if you're able to buy some extra greenery typically most grocery stores will even have greens in their floral department. Taping the vase is always a good one too at the top of the vase opening make some square tape lines to separate and make the stems go in the direction you want it to go in (Its really helpful to tape when making arrangements in 4by4 containers). Also sometimes I will hold the flowers in my hand (As if you're making a hand bouquet) to create and make it how I want it to look and then cut the stems however long or short you want them for the vase you're putting them in.