Put down the scissors
Scissors can cause damage to the stem. Instead, use a sharp, non-serrated knife to cut the bottom of the stems at an angle.
Remove any leaves below the water line
Leaves left below the water line breed bacteria, so make sure you remove them before housing your flowers.
Feed your flowers
There's a reason they give you those little sachets. The tap water you fill your vase with is alkaline, which is also the perfect breeding ground for bacteria. The packet should contain a bleach or an acidifying agent to help reduce the growth of microorganisms in the container.
Look closely at the petals
The more petals that have been removed, the older the flowers are likely to be. It pays to have a closer look before you buy.
Change the water
This a given, but make sure you change the water every other day and also wash the vase out with detergent to remove any bacteria.
Do as a florist would do
An experiment conducted in a controlled environment put a number of theories for keeping flowers fresh to the test. Interestingly, the fridge was the winner. If you have room, place your vase in the fridge over night and bring them out again the next day. Your flowers should last up to seven days.