A simple DIY Valentine's Day paper project: hearts on a string.
Cut colored paper into 3/4" strips. Fold them in half, or if you want some hearts that are twice as big, splice two strips of paper together at the bottom of each heart with double stick tape. Curl the loose ends around a chopstick or pen.
String the heart garland together from the bottom up. I used Sulky clear thread, available at fabric stores. It's curly and hard to see so you have to fight with it a bit, but it turns out nearly invisible. Push your threaded needle up through the bottom fold of each heart, then use double stick tape to sandwich the thread between the two halves of the curled tops.