According to me the most suitable method is take this mixture into a beaker. Make a funnel of filter paper and adjust it on the top of a narrow necked beaker of a bottle. Pass the mixture from the beaker through the filter paper into the bottle. This process will remove sand and pebbles. Then the remaining mixture in the bottle will be of salt and water. Put that mixture on heat so that water evaporate. In this way you can separate the whole mixture. Simple :)
