Asparagus should barely see heat. Simple as that. I have found that blanching and steaming give almost the same results. Either way, the key is not to overcook it.
When blanching asparagus bring the water to a shiver (see Boil) and then add the spears. There should be enough water so that the asparagus is not crowded in the pan.
I start with the asparagus at room temperature and cook for about 2 – 4 minutes depending on the thickness. If you are going to save them for later use refresh them in ice water (see Refreshing Veggies).