I place my dry soil-then add water-just enough to cover the dirt-then I add my dry sand-then I fill with water-drain-repeat until clear-Then with about 3-4inches of water-I plant. Then fill, drain if needed-refill...etc...until clear-usually only take 2-3 water changes-if done correctly.
I use my free hand to divert the water flow so not to kick up the dirt/sand or depending on the hard scape item-I might direct the water flow on it.
I let the water settle for at least 5 min between changes to allow the sand to settle.
I already have my hard scape in place before I add the sand cap
I also might add more sand if needed after I am done and sometimes I will use a small handful of gravel or larger rock at the roots of stem plants to help keep them in place.
I like to plant my rosette plants (swords, crypts, sags, vals..etc...) after the cap-you want their crown to be slightly above the substrate-
Stem plants can be planted before or after the cap-I have found it easier to plant after the cap.
When I make the water changes for setup-I don't drain 100% of the water-I may only remove 50-75%-then refill-this will help avoid too much disturbance of the soil/sand or up-rooting plants.