There are different methods of propagating a string of hearts.
If your plant has them, the tubers (looking like balls/beads) on the string can be planted and will grow into new plants. Put multiple in one pot and you get lots of strings right from the start.
C. woodii will also root from cuttings, 2-3 inch / 8-10 cm sections will work fine. Note that you are working with a succulent, so give the cuttings a few days to dry off before planting or you risk rot. As above, multiple cuttings can go in one pot.
But the probably easiest version is to simply lift the string(s) and place them across the pot (fixing is optional when gravity holds them in place, but you can use some u-shaped wires), where they will typically send out roots at the places that touch the soil. I remember one plant in my mum’s home that got that treatment simply to “stow away” excessively long strands and then grew into a veritable net.