We took it outside and started by asking Caden to pick a letter. Once he did I would ask him what the letter was and then tell him the sound. I would then start saying words that started with the letter. Then Caden would find where the letter goes and put it in the puzzle. It was easy to find the letters at first but towards the end he really had to dig and search. This kept his interest all the way through the alphabet and he still wanted to do more:)
For younger children who aren't working on letters you could put the pieces of any puzzle they have in the rice and have them search around for it.
For an older child you could tell them a letter to search for or just tell them the sound of the letter.
To keep an older child busy you could tell them to find all of the letters in order starting with A and put them in the puzzle.