Always remove any packaging and give the stems a trim by about 1cm it will help the flowers absorb the water quickly
Try and use a clear glass vase so you can keep a check on the water and be 3 quarters full if possible
Remove any leaves that are in they will cause bacteria as they decompose
Always use flower food
if you wouldn’t drink it yourself, then please change the water flowers love fresh, clean water just like us
Lukewarm water is better than cold it contains less oxygen, so it helps limit the bacteria growth by up to 70 to 80 %
Sunny is not funny for your blooms; they like a cool and constant temperature.