I loved doing this when I was learning how to read and write! Have the child say the individual letters as they trace them in the salt/cornmeal, and you're addressing all three learning styles: visual, auditory, and kinesthetic.
The next activity was Missing Letter Name Practice. We started by singing a little song I sing for Jake to teach him how to spell his name. There was a boy that Mama loved and Jacob was his name O, J, A, C, O, B J, A, C, O, B J, A, C, O, B And Jacob was his name O!