First of all find yourself a nice plant from which to take your cutting. A diseased or unhealthy plant is not going to stand much chance of creating anything other than a diseased or unhealthy cutting. Examine the plant and look for a healthy stem that has three pairs of leaves.
Cut the stem a good bit below the third pair of leaves this should ideally give you a cutting of 2 to 3 inches in length. It is now necessary to remove the bottom leaves and trim stem to expose the growing region. Plants major growth areas are in their leaf nodes. This is where the leaves join onto the stem. Take a sharp knife and carefully remove the lowest pair of leaves and the length of stem below the leaf node by cutting 2-3mm below the node.
What you need now is a rooting medium to place your cutting in. A good rooting medium is a seed or multi-purpose compost with either 25% sharp sand, perlite or vermiculite mixed through to provide aeration to the medium. Having said that a novel way of rooting is simply to place them in water at room temperature and they will root, but they don't seem to like the being transferred to compost later and some losses can be expected.
The rooting medium should be quite moist and be placed in a pot or seed tray, so long as it can be covered to maintain a humid atmosphere to sustain the cutting whilst rooting. By all means use a rooting powder if you wish, but I've found this unnecessary. Once your cutting is prepared simply make a small hole with a cocktail stick or something similar and place your cutting in the hole almost up to the next leaf node, and lightly firm. It is best to cover the cutting/s with something transparent to provide good humidity. If you have used a plant pot, an old plastic bottle with the top cut off placed over the pot will do nicely. Room temperature should be good enough for them to root, but it's better if the soil is kept warm, about 60°F an electric propagator is ideal for this.
Once you see fresh green growth in the growing tip, you'll know it's rooting but wait until it starts to visibly grow before removing and potting up.