Cut the flower spike after the flower drops and the stem starts to turn brown. Cut it halfway down the stem. Use a razor sharp blade or pruning shears.
Drip melted candle wax onto the stem to prevent an infection in the cut stem. Alternatively, dust with cinnamon powder.
Care for your plant as usual. Do not move it to a new location, use bark instead of soil and feed sparingly. You will see new flowers in three or four months.