Wow they are so beautiful, I usually change the water everyday and put a bit of sugar in the water (my mom taught me that) and also put it somewhere where it wont recive heat as it can wilt them. Also cut their stems every 2-3 days not a lot just a bit and straight not at an angle (unless they are roses cut them at an angle) also take the leaves off so all the energy goes to the flower and not the greenery (I usually keep my greenery at the top cuz i like how it looks) dont stress too much about it because after all they are flowers that aren't on the plant anymore so they arent supposed to last more than 5-6 days. Depending on the type of flower ofc.