You are going to get some cloudyness no matter what.
To minimize it, get a bag half filled with sand, put water in the bag, mix it up good, pour out the cloudy water, repeat. Then fill the bag back with enough water to just cover the sand and lower the bag into the tank. Slowly pour out the sand on to your tank bottom.
By rinsing you remove lots of the micro sand particles that cloud the water. Be sure to rinse with salt water.