You can either let the leaves dry naturally, or use a food dehydrator to dry the raspberry leaves quicker. First, Then decide how you are going to dry the raspberry leaves:
Hang and Air Dry: Remove the lower leaves, tie the stems into small bundles, and hang upside down in a dry.
Drying Screen: Spread the leaves out on a drying screen. Suspend the screen over two chairs so the air can circulate above and below the screen.
Food Dehydrator: Preheat food dehydrator to 100˚F. Place the herbs in a single layer on dehydrator trays and place in the dehydrator until herbs are dry, 1 to 4 hours depending on the type of herb. Check every 30 minutes to prevent over drying.
Once the leaves are dry, store lightly packed in a glass jar away from direct sunlight. Try not to crush them to reserve the flavor until you are ready to brew your tea.
Store the jars in a in a cool, dark place, away from heat, humidity, and temperature fluctuations. Dried herbs will remain potent for 6 to 12 months when stored properly.
To brew the tea, use about 1-teaspoon of crushed, dried raspberry leaves per 8-ounce cup of boiling water. Steep for at least 5 minutes and drink like regular tea.