Follow the lines
If a vase is tall and thin, aim to follow that direction with your flowers. A popular bloom to add additional height to an arrangement is orchids as the flowering stem adds colour all the way up.
Add some greenery
Foliage makes a wonderful addition to any vase but it can work particularly well when accompanying tall blooms. The green colour makes for a lovely contrast to a monochrome arrangement. Look how the greenery highlights the white blooms here...
