Choose a suitable container for the height and type of flowers. This seems obvious but is one of the main reasons flowers do not thrive due to a lack of support and insufficient water. Make sure the container is spotlessly clean and fill almost to the top with cool fresh water and add the flower food. Flower food helps feed the flowers and keeps the water free of bacteria, but you don’t need to use it.
Strip all the leaves from the bottom half to two-thirds of each stem so that no foliage will be below the water level, this prevents decay which will contaminate the water and reduce the life of the flowers.
Re-cut all stems to the required length, at a sharp angle with sharp scissors or secateurs, this increases the cut surface area and helps with water and nutrient take-up. It also means that the stem base does not lie flat on the vase bottom, unable to take up water.
Check the water level frequently and top up as necessary, at least daily.
Every 2 or 3 days, re-cut the flowers, clean the vase and change the water, removing any flowers which are past their best.
Always place the flowers in a cool position away from direct sunlight, radiators and fires.
If you are trying to get stubborn flowers to open for a special event (lilies and peonies, for example, can take ages to open!) then re-cut the stems and place them in warm/tepid water, repeat every few hours and hopefully, they’ll bloom just in time for everyone arriving.