I love the big mop-top Annabelle hydrangea! Pretty, lacy flowers, that are so delicate. They are super easy to dry, and can even be displayed while you're doing it.
I live in Minnesota, and I've found that the first part of July is the best time to cut them. By this time, the flowers have all bloomed, and they aren't quite as moist as when they first opened. Also, you'll find that there are very few brown flowers on them yet. I like to find some that are a little on the green side for some variation in color.
I cut the stems about 12" long, and remove all of the lower leaves. Fill a large vase with water, and let the hydrangeas sit in the vase until all of the water has gone! That's it.....easy, peasy!!!