You can cut the flowers when you've got a nice bloom -- this is usually at the beginning, rather than the end of each flower's blooming period, when they've got, say, one ring of flowerets -- and hang them upside down to air-dry. The flowerets will then form a kind of "crown" around the top of the flower. But expect the flowerets to shrink a lot in the process.

You can also wait until the flowers are past, and dry what is now the seed head.

Some people dry the flowers upright. I haven't had good results with this method myself, but you can never tell.

I've noticed a lot of difference between different monardas. Of my regular garden types, the scarlets do much better than the violets.

Some of my best luck has been with what I think is some form of M. fistulosa, although as I remember the seed was billed as M. bradburiana. It's a low-growing type, just a little bit over a foot tall, and it blooms early. But some of the plants have very deep purple/burgundy foliage and seed heads (all have pale lavender flowers). The foliage air-dries very nicely and the plants are very effective in bouquets with or without the flowerets.