Think beyond the vase! If you have a vase of flowers on a dining table for a quick dinner party, think about scattering flower petals, leaves, or even fruit along the tabletop.
If you're in an urban city like New York, the corner markets are fantastic sources for tulips and roses.
People overthink flowers. They are afraid to mix and match, so they don't do anything!
There is no such thing as a Flower Police, so please feel free to experiment. Or stick with one type of flower; for instance, do bunches of white tulips or a mix of flowers that are all yellow in color. Just because it's simple doesn't mean it can't be dramatic!
I love paperwhites - they smell heavenly and you can often pick them up from a big home improvement store garden center already planted in pretty terra cotta pots.