An airing cupboard or any warm dark place is the ideal place to dry herbs, including the flowers and some fruits. The first step is to wash all parts of the plant thoroughly, pat dry between kitchen towel and remove any unwanted or bad parts.
Next take a box and line the bottom with kitchen towel, on top of this place a layer of what ever it is that you are drying and then another layer of kitchen towel on top, place in airing cupboard or any other appropriate place until dried.
Clean the box and place on a nice flat surface.
Line the box with paper.
Spread the herb out as evenly and thinly as possible. Pick out any dead bits.
Cover with a few sheets of newspaper
Place in a dark and dry place like an airing cupboard, or near some hot pipes.
Check your herbs for mould every day or two, it will take about a week for all of the flowers to dry.
How to Dry Herbs in Bunches
Another way to dry herbs, is to hang bunches upside down until they become brittle, but not too dry so that they crumble, at this point you can strip the stalks of leaves and flowers, and then keep in an air tight jar.
Hang the drying bundles anywhere warm and dry, but out of direct sunlight. This could be indoors or out, depending on the area. I use a small cupboard to dry my herb bunches, this also contains my boiler, so it's nice and dry.
If you are worried about of the dried herb falling or being blown away you can place a paper bag round each bundle of herbs before hanging to dry, Just tie the gathered ends of the bag around the herb stalks - the bag will catch any falling leaves or flowers.
Make sure to check on your hanging bundles daily, as the plants dry, the string will become loose and need re-tying. Even my most tightly tied bundles need re-tying at least 3 times during the drying process.
I like to label the herbs I hang up to dry, sometimes as the leaves curl up it can be hard to identify each plant by sight. I usually label my mints as these can get confusing as they dry.