It is quite straight forward to dry flowers at home, although results vary, so experimentation is always a good idea. Collect a bunch of your favourite flowers, tie together loosely, then hang upside down somewhere where there is good air circulation. The airing cupboard offers fast results, but a garage or even an open porch can be effective, although the process may take longer. Drying in a bright greenhouse may not be as suitable, because although the flowers dry quickly, they may also loose some of their bright colours in the strong sunlight.
If you only want to dry the flower heads, try laying the flowers flat on shelves in your airing cupboard (or if you’re keen, make purpose built trays consisting of a wooden frame and base of wire mesh for the best air circulation). Make sure you arrange each flower how you want it at the beginning, because it will be too brittle to tweak once it has dried!
Alternative home air drying methods include using the oven. Laying blooms on a baking tray in a low (30C) oven overnight can work, and is particularly good for drying fruit slices such as orange slices, and flat objects.
It is also possible to use a microwave oven for drying flowers in combination with a desiccant such as silica gel, which is something I am experimenting with at the moment. Dry flowers using silica gel.
Commercially, air drying is used for crops such as lavender bunches where the bunches are hung up in barns to dry (in France & the UK for example). Rose petals in Iran are laid out on large tables or sheets to dry in the warm ambient air. Unfortunately, air drying usually causes brittleness, and for this reason, some flowers are preserved using freeze drying techniques requiring specialist equipment, or are impregnated with a liquid preservative.
The roses in the picture arrived courtesy of my husband in a Valentines Day bouquet. I enjoyed them fresh in a vase for a week, then when they started to fade, I tied them together at the bottom with an elastic band and hung them up in my airing cupboard. They only took a week to dry in there, and now I can enjoy them as dried flowers for a few more months!