The three secrets of success in growing flowers.

Without oversimplifying,  most flower woes can be  prevented if proper attention if given to these three areas:Soil.  Sun and Sustenance.
Let's start with soil.  Before you even begin to plant, you need to know the needs of your plant.  What type of soil does it need?  All dirt is not the same.
Next, you need to know how much sun  your flower needs.  And, you need to be fully acquainted with the amount of light your garden receives in each square foot.  Really.
After you nail this down, you need to research the nutritional needs of your plant.  Much plant feeding needs to begin at planting time, around the roots of the plant.  This is really important, especially with heavy feeders. Naturally, the nutritional needs vary from plant to plant.
Finally, hydration and humidity.
Have I scared you yet? Great then, read on.
Soil.  Type of, location of, drainage, aeration,
Sun.  Full, some, shade, none
Sustenance.   (Food and water).   The three letters of nutrition.  Basic watering 101
Common watering problems.