I have a flower garden out back. I love cut flowers. I hate to see them die, so I try and preserve them as long as possible inside.
After bringing them inside I always cut the stems at an angle under water. I remove all leaves that will be under water. I make sure my vase is extra clean and free of harmful bacteria. I add plant food from the florist or I drop two non-coated aspirin into my water or if I don't have either of these items, I will add about four pennies to my water. Now I put my flowers into the vase. Make sure not to place flowers in direct heat or sun light. Flowers need a very cool place if you want them to last. I also change my water as often as possible.
Hope this is helpful!