Don't just think about your friends, write to them! Whether an ecard, a store bought card or a homemade one, reach out to a friend and make their day.
The origins of this day are not known, but it's celebrated every year. Take the opportunity to meet someone new by taking a chance and just saying hello to someone in the park, or join an interest group. New friends can open up new horizons and opportunities and are one of life's valuable assets.