To propagate by soil-layering use the following steps;

1. Locate a suitable stem as previously mentioned find a leggy, pliable stem that grows leaves along it.
2. Make an underside incision find a place along the stem that can bend low enough to reach the ground. Make an incision on the part of the stem that touches the soil as at upward slant, taking care not to cut through more than 1/3 of the stem.
3. Dust with hormone powder I have never used this with soil-layering and have nearly always had success but if you're find that you don't want to risk the result use a little of the powder or gel around the cut.
4. Remove some soil scoop enough topsoil to create a small trench for the stem to lay along. Lay the stem down and then cover again with remaining soil.
5. Hold the stem down use a metal "U" turned upside down to hold the stem in the soil. The only time you will fail with this technique is when the stem comes away from the soil and air affects the incision.

As an alternative, you can use a pot to grow the plant in by replacing the soil method with some potting mix in a container.