Article in English: Cut them right at their peak, when their color and scent are strongest. This will ensure they'll last as long as possible in your flower arrangement. Place them in a vase of clean water immediately. Gather a bunch of freshly harvested lilacs and bind their stems with a rubber band. Hang them upside down in a cool, dark place for 1 – 3 weeks. Gently remove the rubber band when the lilacs are completely dry.  Dry lilacs using silica gel. Fill a large glass or plastic container with an inch of silica gel. Place a few stems of freshly harvested lilac into the container so that they stand up in the gel. Fill the rest of the container with gel so that it completely covers the lilac. Put a lid on the container and wait a week or so for the lilacs to dry. Remove them from the jar and use them in a flower arrangement.

Summary in Chinese:
在丁香花开得最盛的时候将其剪下来。 把丁香花倒挂起来晾干。