Never, Never, Never rules for flower care!

Never..

.. break, crush or split the stems! This encourages bacteria to grow, which stops the flowers drinking the water and absorbing the nutrients they need.
.. put Daffodils in mixed arrangements. Daffs release a latex slime that harms other flowers. Use the specialist bulb cut flower food to counteract this.
.. put flowers near fruit and vegetables, or mix (nearly) dying flowers with fresh ones. Older flowers, fruit and vegetables all release ethylene gas which prematurely ages fresh flowers.
.. put coins, lemonade, sugar, aspirin or bleach in the water. They waste your money, don’t do your flowers any good and may shorten their life considerably.