The so-called live sand with water in the bag is a rip-off IMO.
I premixed my water before I put it in my tank, it kind of gave me some practice in getting the salinity and temp right, before I added. I agree with austinsdad, as well, but have found sometimes the salt has "stuff" in it that does not dissolve.
If I were starting a new tank, I would premix the water, add the sand (like austinsdad said, if it is dry, rinse it well, to get rid of the dust), add the LR
, softly shift it so that most of the bottom of the LR
piece is resting against the bottom of the tank, then add the water, slowly.