Hand wash, never the dishwasher. Wash the blade by hand with warm water and a little soap, then dry it straight away with a soft cloth. The dishwasher dulls the edge and damages the handle.
Cut on wood or plastic. Use a wooden or plastic board. Glass, stone, granite, and ceramic will chip a fine edge.
Hone often, sharpen rarely. A few passes on a honing rod every week or two keeps the edge true. When it finally needs sharpening, any standard whetstone suited to Japanese-style knives restores it.
Store it safely. Keep the knife on a magnetic strip, in a saya, or in a block, not loose in a drawer where the edge can knock against other tools.
Keep it dry. Never leave the knife to soak or sit wet in the sink. A drop of food-safe oil before long storage protects both the steel and the Damascus pattern.