There are two keys to setting your flowers up for the longest possible vase life:
1) Hydration: Flowers *love* fresh, clean water. Forget the penny, the lemon + sugar, the flower food - Just change that water daily, and give the stems a good clip every couple days! If your flowers have been deprived for a while, give them room temp water. After that, switch to cool water for all subsequent changes.
2) Temperature: Flowers can be enjoyed anywhere in your home - but they will last the longest if they are stored out of direct sun, and wherever in your home is coolest.