You will need:
a large paper clip
a necklace jump ring
The first thing you need to do is open the paper clip so that it look like a heart. There are several ways to do this, if you separate the paper clip just a little bit, it will be an overlapping heart, or you can pull it completely apart and shape it into a heart as in these photos.
Start wrapping the paper clip in twine. The goal is to completely cover the paper clip with twine. As you wrap, dip your fingers in glue and spread it over the twine as you go. Cementing the twine together.
Allow the heart to dry completely and then add a jump ring to it so it can be worn as a necklace. This necklace turned out better than I expected it too, in fact, after I gave it to my four-year-old, I decided I liked it so much that I needed to make myself one. It is the perfect Valentine-y necklace with bonus points for being made out of stuff I had on hand.